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<button class="button is-small is-link">Go</button> </div> </div> </form> </div> </div> <ol class="breathe-horizontal" start="1"> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2409.02695">arXiv:2409.02695</a> <span> [<a href="https://arxiv.org/pdf/2409.02695">pdf</a>, <a href="https://arxiv.org/format/2409.02695">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/ad77a0">10.3847/1538-4357/ad77a0 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> How does the critical torus instability height vary with the solar cycle? </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=James%2C+A+W">Alexander W. James</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Barnes%2C+G">Graham Barnes</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">Lidia van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Williams%2C+D+R">David R. Williams</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2409.02695v1-abstract-short" style="display: inline;"> The ideal magnetohydrodynamic torus instability can drive the eruption of coronal mass ejections. The critical threshold of magnetic field strength decay for the onset of the torus instability occurs at different heights in different solar active regions, and understanding this variation could therefore improve space weather prediction. In this work, we aim to find out how the critical torus insta… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2409.02695v1-abstract-full').style.display = 'inline'; document.getElementById('2409.02695v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2409.02695v1-abstract-full" style="display: none;"> The ideal magnetohydrodynamic torus instability can drive the eruption of coronal mass ejections. The critical threshold of magnetic field strength decay for the onset of the torus instability occurs at different heights in different solar active regions, and understanding this variation could therefore improve space weather prediction. In this work, we aim to find out how the critical torus instability height evolves throughout the solar activity cycle. We study a significant subset of HMI and MDI Space-Weather HMI Active Region Patches (SHARPs and SMARPs) from 1996-2023, totalling 21584 magnetograms from 4436 unique active region patches. For each magnetogram, we compute the critical height averaged across the main polarity inversion line, the total unsigned magnetic flux and the separation between the positive and negative magnetic polarities. We find the critical height in active regions varies with the solar cycle, with higher (lower) average critical heights observed around solar maximum (minimum). We conclude this is because the critical height is proportional to the separation between opposite magnetic polarities, which in turn is proportional to the total magnetic flux in a region, and more magnetic regions with larger fluxes and larger sizes are observed at solar maximum. This result is noteworthy because, despite the higher critical heights, more CMEs are observed around solar maximum than at solar minimum. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2409.02695v1-abstract-full').style.display = 'none'; document.getElementById('2409.02695v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 4 September, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2024. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Accepted to ApJ. 14 pages, 6 Figures, 1 Table</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2405.10810">arXiv:2405.10810</a> <span> [<a href="https://arxiv.org/pdf/2405.10810">pdf</a>, <a href="https://arxiv.org/format/2405.10810">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Space Physics">physics.space-ph</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> </div> <p class="title is-5 mathjax"> Flux rope modeling of the 2022 Sep 5 CME observed by Parker Solar Probe and Solar Orbiter from 0.07 to 0.69 au </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Davies%2C+E+E">Emma E. Davies</a>, <a href="/search/astro-ph?searchtype=author&query=R%C3%BCdisser%2C+H+T">Hannah T. R眉disser</a>, <a href="/search/astro-ph?searchtype=author&query=Amerstorfer%2C+U+V">Ute V. Amerstorfer</a>, <a href="/search/astro-ph?searchtype=author&query=M%C3%B6stl%2C+C">Christian M枚stl</a>, <a href="/search/astro-ph?searchtype=author&query=Bauer%2C+M">Maike Bauer</a>, <a href="/search/astro-ph?searchtype=author&query=Weiler%2C+E">Eva Weiler</a>, <a href="/search/astro-ph?searchtype=author&query=Amerstorfer%2C+T">Tanja Amerstorfer</a>, <a href="/search/astro-ph?searchtype=author&query=Majumdar%2C+S">Satabdwa Majumdar</a>, <a href="/search/astro-ph?searchtype=author&query=Hess%2C+P">Phillip Hess</a>, <a href="/search/astro-ph?searchtype=author&query=Weiss%2C+A+J">Andreas J. Weiss</a>, <a href="/search/astro-ph?searchtype=author&query=Reiss%2C+M+A">Martin A. Reiss</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Long%2C+D+M">David M. Long</a>, <a href="/search/astro-ph?searchtype=author&query=Nieves-Chinchilla%2C+T">Teresa Nieves-Chinchilla</a>, <a href="/search/astro-ph?searchtype=author&query=Trotta%2C+D">Domenico Trotta</a>, <a href="/search/astro-ph?searchtype=author&query=Horbury%2C+T+S">Timothy S. Horbury</a>, <a href="/search/astro-ph?searchtype=author&query=O%27Brien%2C+H">Helen O'Brien</a>, <a href="/search/astro-ph?searchtype=author&query=Fauchon-Jones%2C+E">Edward Fauchon-Jones</a>, <a href="/search/astro-ph?searchtype=author&query=Morris%2C+J">Jean Morris</a>, <a href="/search/astro-ph?searchtype=author&query=Owen%2C+C+J">Christopher J. Owen</a>, <a href="/search/astro-ph?searchtype=author&query=Bale%2C+S+D">Stuart D. Bale</a>, <a href="/search/astro-ph?searchtype=author&query=Kasper%2C+J+C">Justin C. Kasper</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2405.10810v2-abstract-short" style="display: inline;"> As both Parker Solar Probe (PSP) and Solar Orbiter (SolO) reach heliocentric distances closer to the Sun, they present an exciting opportunity to study the structure of CMEs in the inner heliosphere. We present an analysis of the global flux rope structure of the 2022 September 5 CME event that impacted PSP at a heliocentric distance of only 0.07 au and SolO at 0.69 au. We compare in situ measurem… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.10810v2-abstract-full').style.display = 'inline'; document.getElementById('2405.10810v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2405.10810v2-abstract-full" style="display: none;"> As both Parker Solar Probe (PSP) and Solar Orbiter (SolO) reach heliocentric distances closer to the Sun, they present an exciting opportunity to study the structure of CMEs in the inner heliosphere. We present an analysis of the global flux rope structure of the 2022 September 5 CME event that impacted PSP at a heliocentric distance of only 0.07 au and SolO at 0.69 au. We compare in situ measurements at PSP and SolO to determine global and local expansion measures, finding a good agreement between magnetic field relationships with heliocentric distance, but significant differences with respect to flux rope size. We use PSP/WISPR images as input to the ELEvoHI model, providing a direct link between remote and in situ observations; we find a large discrepancy between the resulting modeled arrival times, suggesting that the underlying model assumptions may not be suitable when using data obtained close to the Sun, where the drag regime is markedly different in comparison to larger heliocentric distances. Finally, we fit the SolO/MAG and PSP/FIELDS data independently with the 3DCORE model and find that many parameters are consistent between spacecraft, however, challenges are apparent when reconstructing a global 3D structure that aligns with arrival times at PSP and Solar Orbiter, likely due to the large radial and longitudinal separations between spacecraft. From our model results, it is clear the solar wind background speed and drag regime strongly affect the modeled expansion and propagation of CMEs and need to be taken into consideration. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.10810v2-abstract-full').style.display = 'none'; document.getElementById('2405.10810v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 19 July, 2024; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 17 May, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2024. </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2405.07755">arXiv:2405.07755</a> <span> [<a href="https://arxiv.org/pdf/2405.07755">pdf</a>, <a href="https://arxiv.org/format/2405.07755">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> </div> <p class="title is-5 mathjax"> Searching for evidence of subchromospheric magnetic reconnection on the Sun </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Baker%2C+D">D. Baker</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">L. van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=James%2C+A+W">A. W. James</a>, <a href="/search/astro-ph?searchtype=author&query=Demoulin%2C+P">P. Demoulin</a>, <a href="/search/astro-ph?searchtype=author&query=To%2C+A+S+H">A. S. H. To</a>, <a href="/search/astro-ph?searchtype=author&query=Murabito%2C+M">M. Murabito</a>, <a href="/search/astro-ph?searchtype=author&query=Long%2C+D+M">D. M. Long</a>, <a href="/search/astro-ph?searchtype=author&query=Brooks%2C+D+H">D. H. Brooks</a>, <a href="/search/astro-ph?searchtype=author&query=McKevitt%2C+J">J. McKevitt</a>, <a href="/search/astro-ph?searchtype=author&query=Laming%2C+J+M">J. M. Laming</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Yardley%2C+S+L">S. L. Yardley</a>, <a href="/search/astro-ph?searchtype=author&query=Valori%2C+G">G. Valori</a>, <a href="/search/astro-ph?searchtype=author&query=Mihailescu%2C+T">T. Mihailescu</a>, <a href="/search/astro-ph?searchtype=author&query=Matthews%2C+S+A">S. A. Matthews</a>, <a href="/search/astro-ph?searchtype=author&query=Kuniyoshi%2C+H">H. Kuniyoshi</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2405.07755v1-abstract-short" style="display: inline;"> Within the coronae of stars, abundances of those elements with low first ionization potential (FIP) often differ from their photospheric values. The coronae of the Sun and solar-type stars mostly show enhancements of low-FIP elements (the FIP effect) while more active stars such as M dwarfs have coronae generally characterized by the inverse-FIP (I-FIP) effect. Highly localized regions of I-FIP ef… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.07755v1-abstract-full').style.display = 'inline'; document.getElementById('2405.07755v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2405.07755v1-abstract-full" style="display: none;"> Within the coronae of stars, abundances of those elements with low first ionization potential (FIP) often differ from their photospheric values. The coronae of the Sun and solar-type stars mostly show enhancements of low-FIP elements (the FIP effect) while more active stars such as M dwarfs have coronae generally characterized by the inverse-FIP (I-FIP) effect. Highly localized regions of I-FIP effect solar plasma have been observed by Hinode/EIS in a number of highly complex active regions, usually around strong light bridges of the umbrae of coalescing/merging sunspots. These observations can be interpreted in the context of the ponderomotive force fractionation model which predicts that plasma with I-FIP effect composition is created by the refraction of waves coming from below the plasma fractionation region in the chromosphere. A plausible source of these waves is thought to be reconnection in the (high-plasma \b{eta}) subchromospheric magnetic field. In this study, we use the 3D visualization technique of Chintzoglou & Zhang (2013) combined with observations of localized I-FIP effect in the corona of AR 11504 to identify potential sites of such reconnection and its possible consequences in the solar atmosphere. We found subtle signatures of episodic heating and reconnection outflows in the expected places, in between magnetic flux tubes forming a light bridge, within the photosphere of the active region. Furthermore, on either side of the light bridge, we observed small antiparallel horizontal magnetic field components supporting the possibility of reconnection occuring where we observe I-FIP plasma. When taken together with the I-FIP effect observations, these subtle signatures provide a compelling case for indirect observational evidence of reconnection below the fractionation layer of the chromosphere, however, direct evidence remains elusive. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.07755v1-abstract-full').style.display = 'none'; document.getElementById('2405.07755v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 13 May, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2024. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Accepted ApJ</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2310.13677">arXiv:2310.13677</a> <span> [<a href="https://arxiv.org/pdf/2310.13677">pdf</a>, <a href="https://arxiv.org/format/2310.13677">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> </div> <p class="title is-5 mathjax"> Intriguing Plasma Composition Pattern in a Solar Active Region: a Result of Non-Resonant Alfv茅n Waves? </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Mihailescu%2C+T">Teodora Mihailescu</a>, <a href="/search/astro-ph?searchtype=author&query=Brooks%2C+D+H">David H. Brooks</a>, <a href="/search/astro-ph?searchtype=author&query=Laming%2C+J+M">J. Martin Laming</a>, <a href="/search/astro-ph?searchtype=author&query=Baker%2C+D">Deborah Baker</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=James%2C+A+W">Alexander W. James</a>, <a href="/search/astro-ph?searchtype=author&query=Long%2C+D+M">David M. Long</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">Lidia van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Stangalini%2C+M">Marco Stangalini</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2310.13677v1-abstract-short" style="display: inline;"> The plasma composition of the solar corona is different from that of the solar photosphere. Elements that have a low first ionisation potential (FIP) are preferentially transported to the corona and, therefore, show enhanced abundances in the corona compared to the photosphere. The level of enhancement is measured using the FIP bias parameter. In this work, we use data from the EUV Imaging Spectro… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2310.13677v1-abstract-full').style.display = 'inline'; document.getElementById('2310.13677v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2310.13677v1-abstract-full" style="display: none;"> The plasma composition of the solar corona is different from that of the solar photosphere. Elements that have a low first ionisation potential (FIP) are preferentially transported to the corona and, therefore, show enhanced abundances in the corona compared to the photosphere. The level of enhancement is measured using the FIP bias parameter. In this work, we use data from the EUV Imaging Spectrometer (EIS) on Hinode to study the plasma composition in an active region following an episode of significant new flux emergence into the pre-existing magnetic environment of the active region. We use two FIP bias diagnostics: Si X 258.375 A/S X 264.233 A (temperature of approximately 1.5 MK) and Ca XIV 193.874 A/Ar XIV 194.396 A (temperature of approximately 4 MK). We observe slightly higher FIP bias values with the Ca/Ar diagnostic than Si/S in the newly emerging loops, and this pattern is much stronger in the preexisting loops (those that had been formed before the flux emergence). This result can be interpreted in the context of the ponderomotive force model, which proposes that the plasma fractionation is generally driven by Alfv茅n waves. Model simulations predict this difference between diagnostics using simple assumptions about the wave properties, particularly that the fractionation is driven by resonant/non-resonant waves in the emerging/preexisting loops. We propose that this results in the different fractionation patterns observed in these two sets of loops. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2310.13677v1-abstract-full').style.display = 'none'; document.getElementById('2310.13677v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 20 October, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> October 2023. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Accepted for publication in The Astrophysical Journal</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2308.14651">arXiv:2308.14651</a> <span> [<a href="https://arxiv.org/pdf/2308.14651">pdf</a>, <a href="https://arxiv.org/format/2308.14651">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> </div> <p class="title is-5 mathjax"> The eruption of a magnetic flux rope observed by \textit{Solar Orbiter} and \textit{Parker Solar Probe} </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Long%2C+D+M">David M. Long</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Pecora%2C+F">Francesco Pecora</a>, <a href="/search/astro-ph?searchtype=author&query=Brooks%2C+D+H">David H. Brooks</a>, <a href="/search/astro-ph?searchtype=author&query=Strecker%2C+H">Hanna Strecker</a>, <a href="/search/astro-ph?searchtype=author&query=Orozco-Su%C3%A1rez%2C+D">David Orozco-Su谩rez</a>, <a href="/search/astro-ph?searchtype=author&query=Hayes%2C+L+A">Laura A. Hayes</a>, <a href="/search/astro-ph?searchtype=author&query=Davies%2C+E+E">Emma E. Davies</a>, <a href="/search/astro-ph?searchtype=author&query=Amerstorfer%2C+U+V">Ute V. Amerstorfer</a>, <a href="/search/astro-ph?searchtype=author&query=Mierla%2C+M">Marilena Mierla</a>, <a href="/search/astro-ph?searchtype=author&query=Lario%2C+D">David Lario</a>, <a href="/search/astro-ph?searchtype=author&query=Berghmans%2C+D">David Berghmans</a>, <a href="/search/astro-ph?searchtype=author&query=Zhukov%2C+A+N">Andrei N. Zhukov</a>, <a href="/search/astro-ph?searchtype=author&query=R%C3%BCdisser%2C+H+T">Hannah T. R眉disser</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2308.14651v1-abstract-short" style="display: inline;"> Magnetic flux ropes are a key component of coronal mass ejections, forming the core of these eruptive phenomena. However, determining whether a flux rope is present prior to eruption onset and, if so, the rope's handedness and the number of turns that any helical field lines make is difficult without magnetic field modelling or in-situ detection of the flux rope. We present two distinct observatio… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2308.14651v1-abstract-full').style.display = 'inline'; document.getElementById('2308.14651v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2308.14651v1-abstract-full" style="display: none;"> Magnetic flux ropes are a key component of coronal mass ejections, forming the core of these eruptive phenomena. However, determining whether a flux rope is present prior to eruption onset and, if so, the rope's handedness and the number of turns that any helical field lines make is difficult without magnetic field modelling or in-situ detection of the flux rope. We present two distinct observations of plasma flows along a filament channel on 4 and 5 September 2022 made using the \textit{Solar Orbiter} spacecraft. Each plasma flow exhibited helical motions in a right-handed sense as the plasma moved from the source active region across the solar disk to the quiet Sun, suggesting that the magnetic configuration of the filament channel contains a flux rope with positive chirality and at least one turn. The length and velocity of the plasma flow increased from the first to the second observation, suggesting evolution of the flux rope, with the flux rope subsequently erupting within $\sim$5~hours of the second plasma flow. The erupting flux rope then passed over the \textit{Parker Solar Probe} spacecraft during its Encounter 13, enabling \textit{in-situ} diagnostics of the structure. Although complex and consistent with the flux rope erupting from underneath the heliospheric current sheet, the \textit{in-situ} measurements support the inference of a right-handed flux rope from remote-sensing observations. These observations provide a unique insight into the eruption and evolution of a magnetic flux rope near the Sun. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2308.14651v1-abstract-full').style.display = 'none'; document.getElementById('2308.14651v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 28 August, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2023. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">19 pages, 11 figures, accepted for publication in The Astrophysical Journal</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2305.06106">arXiv:2305.06106</a> <span> [<a href="https://arxiv.org/pdf/2305.06106">pdf</a>, <a href="https://arxiv.org/format/2305.06106">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/acd44e">10.3847/1538-4357/acd44e <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The Merging of a Coronal Dimming and the Southern Polar Coronal Hole </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Ngampoopun%2C+N">Nawin Ngampoopun</a>, <a href="/search/astro-ph?searchtype=author&query=Long%2C+D+M">David M. Long</a>, <a href="/search/astro-ph?searchtype=author&query=Baker%2C+D">Deborah Baker</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Yardley%2C+S+L">Stephanie L. Yardley</a>, <a href="/search/astro-ph?searchtype=author&query=James%2C+A+W">Alexander W. James</a>, <a href="/search/astro-ph?searchtype=author&query=To%2C+A+S+H">Andy S. H. To</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2305.06106v1-abstract-short" style="display: inline;"> We report on the merging between the southern polar coronal hole and an adjacent coronal dimming induced by a coronal mass ejection on 2022 March 18, resulting in the merged region persisting for at least 72 hrs. We use remote sensing data from multiple co-observing spacecraft to understand the physical processes during this merging event. The evolution of the merger is examined using Extreme-Ultr… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2305.06106v1-abstract-full').style.display = 'inline'; document.getElementById('2305.06106v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2305.06106v1-abstract-full" style="display: none;"> We report on the merging between the southern polar coronal hole and an adjacent coronal dimming induced by a coronal mass ejection on 2022 March 18, resulting in the merged region persisting for at least 72 hrs. We use remote sensing data from multiple co-observing spacecraft to understand the physical processes during this merging event. The evolution of the merger is examined using Extreme-UltraViolet (EUV) images obtained from the Atmospheric Imaging Assembly onboard the Solar Dynamic Observatory and Extreme Ultraviolet Imager onboard the Solar Orbiter spacecraft. The plasma dynamics are quantified using spectroscopic data obtained from the EUV Imaging Spectrometer onboard Hinode. The photospheric magnetograms from the Helioseismic and Magnetic Imager are used to derive magnetic field properties. To our knowledge, this work is the first spectroscopical analysis of the merging of two open-field structures. We find that the coronal hole and the coronal dimming become indistinguishable after the merging. The upflow speeds inside the coronal dimming become more similar to that of a coronal hole, with a mixture of plasma upflows and downflows observable after the merging. The brightening of bright points and the appearance of coronal jets inside the merged region further imply ongoing reconnection processes. We propose that component reconnection between the coronal hole and coronal dimming fields plays an important role during this merging event, as the footpoint switching resulting from the reconnection allows the coronal dimming to intrude onto the boundary of the southern polar coronal hole. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2305.06106v1-abstract-full').style.display = 'none'; document.getElementById('2305.06106v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 10 May, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2023. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">17 pages, 8 figures, accepted for publication in The Astrophysical Journal</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2304.09570">arXiv:2304.09570</a> <span> [<a href="https://arxiv.org/pdf/2304.09570">pdf</a>, <a href="https://arxiv.org/format/2304.09570">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Space Physics">physics.space-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4365/acd24b">10.3847/1538-4365/acd24b <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Slow Solar Wind Connection Science during Solar Orbiter's First Close Perihelion Passage </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Yardley%2C+S+L">Stephanie L. Yardley</a>, <a href="/search/astro-ph?searchtype=author&query=Owen%2C+C+J">Christopher J. Owen</a>, <a href="/search/astro-ph?searchtype=author&query=Long%2C+D+M">David M. Long</a>, <a href="/search/astro-ph?searchtype=author&query=Baker%2C+D">Deborah Baker</a>, <a href="/search/astro-ph?searchtype=author&query=Brooks%2C+D+H">David H. Brooks</a>, <a href="/search/astro-ph?searchtype=author&query=Polito%2C+V">Vanessa Polito</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Matthews%2C+S">Sarah Matthews</a>, <a href="/search/astro-ph?searchtype=author&query=Owens%2C+M">Mathew Owens</a>, <a href="/search/astro-ph?searchtype=author&query=Lockwood%2C+M">Mike Lockwood</a>, <a href="/search/astro-ph?searchtype=author&query=Stansby%2C+D">David Stansby</a>, <a href="/search/astro-ph?searchtype=author&query=James%2C+A+W">Alexander W. James</a>, <a href="/search/astro-ph?searchtype=author&query=Valori%2C+G">Gherado Valori</a>, <a href="/search/astro-ph?searchtype=author&query=Giunta%2C+A">Alessandra Giunta</a>, <a href="/search/astro-ph?searchtype=author&query=Janvier%2C+M">Miho Janvier</a>, <a href="/search/astro-ph?searchtype=author&query=Ngampoopun%2C+N">Nawin Ngampoopun</a>, <a href="/search/astro-ph?searchtype=author&query=Mihailescu%2C+T">Teodora Mihailescu</a>, <a href="/search/astro-ph?searchtype=author&query=To%2C+A+S+H">Andy S. H. To</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">Lidia van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Demoulin%2C+P">Pascal Demoulin</a>, <a href="/search/astro-ph?searchtype=author&query=D%27Amicis%2C+R">Raffaella D'Amicis</a>, <a href="/search/astro-ph?searchtype=author&query=French%2C+R+J">Ryan J. French</a>, <a href="/search/astro-ph?searchtype=author&query=Suen%2C+G+H+H">Gabriel H. H. Suen</a>, <a href="/search/astro-ph?searchtype=author&query=Roulliard%2C+A+P">Alexis P. Roulliard</a>, <a href="/search/astro-ph?searchtype=author&query=Pinto%2C+R+F">Rui F. Pinto</a> , et al. (54 additional authors not shown) </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2304.09570v2-abstract-short" style="display: inline;"> The Slow Solar Wind Connection Solar Orbiter Observing Plan (Slow Wind SOOP) was developed to utilise the extensive suite of remote sensing and in situ instruments on board the ESA/NASA Solar Orbiter mission to answer significant outstanding questions regarding the origin and formation of the slow solar wind. The Slow Wind SOOP was designed to link remote sensing and in situ measurements of slow w… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2304.09570v2-abstract-full').style.display = 'inline'; document.getElementById('2304.09570v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2304.09570v2-abstract-full" style="display: none;"> The Slow Solar Wind Connection Solar Orbiter Observing Plan (Slow Wind SOOP) was developed to utilise the extensive suite of remote sensing and in situ instruments on board the ESA/NASA Solar Orbiter mission to answer significant outstanding questions regarding the origin and formation of the slow solar wind. The Slow Wind SOOP was designed to link remote sensing and in situ measurements of slow wind originating at open-closed field boundaries. The SOOP ran just prior to Solar Orbiter's first close perihelion passage during two remote sensing windows (RSW1 and RSW2) between 2022 March 3-6 and 2022 March 17-22, while Solar Orbiter was at a heliocentric distance of 0.55-0.51 and 0.38-0.34 au from the Sun, respectively. Coordinated observation campaigns were also conducted by Hinode and IRIS. The magnetic connectivity tool was used, along with low latency in situ data, and full-disk remote sensing observations, to guide the target pointing of Solar Orbiter. Solar Orbiter targeted an active region complex during RSW1, the boundary of a coronal hole, and the periphery of a decayed active region during RSW2. Post-observation analysis using the magnetic connectivity tool along with in situ measurements from MAG and SWA/PAS, show that slow solar wind, with velocities between 210 and 600 km/s, arrived at the spacecraft originating from two out of the three of the target regions. The Slow Wind SOOP, despite presenting many challenges, was very successful, providing a blueprint for planning future observation campaigns that rely on the magnetic connectivity of Solar Orbiter. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2304.09570v2-abstract-full').style.display = 'none'; document.getElementById('2304.09570v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 20 April, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 19 April, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2023. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">24 pages, 10 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2208.12774">arXiv:2208.12774</a> <span> [<a href="https://arxiv.org/pdf/2208.12774">pdf</a>, <a href="https://arxiv.org/format/2208.12774">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Space Physics">physics.space-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/ac8d69">10.3847/1538-4357/ac8d69 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The magnetic field environment of active region 12673 that produced the energetic particle events of September 2017 </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Yardley%2C+S+L">Stephanie L. Yardley</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=James%2C+A+W">Alexander W. James</a>, <a href="/search/astro-ph?searchtype=author&query=Stansby%2C+D">David Stansby</a>, <a href="/search/astro-ph?searchtype=author&query=Mihailescu%2C+T">Teodora Mihailescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2208.12774v2-abstract-short" style="display: inline;"> Forecasting solar energetic particles (SEPs), and identifying flare/CMEs from active regions (ARs) that will produce SEP events in advance is extremely challenging. We investigate the magnetic field environment of AR 12673, including the AR's magnetic configuration, the surrounding field configuration in the vicinity of the AR, the decay index profile, and the footpoints of Earth-connected magneti… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2208.12774v2-abstract-full').style.display = 'inline'; document.getElementById('2208.12774v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2208.12774v2-abstract-full" style="display: none;"> Forecasting solar energetic particles (SEPs), and identifying flare/CMEs from active regions (ARs) that will produce SEP events in advance is extremely challenging. We investigate the magnetic field environment of AR 12673, including the AR's magnetic configuration, the surrounding field configuration in the vicinity of the AR, the decay index profile, and the footpoints of Earth-connected magnetic field, around the time of four eruptive events. Two of the eruptive events are SEP-productive (2017 September 4 at 20:00~UT and September 6 at 11:56~UT), while two are not (September 4 at 18:05~UT and September 7 at 14:33~UT). We analysed a range of EUV and white-light coronagraph observations along with potential field extrapolations and find that the CMEs associated with the SEP-productive events either trigger null point reconnection that redirects flare-accelerated particles from the flare site to the Earth-connected field and/or have a significant expansion (and shock formation) into the open Earth-connected field. The rate of change of the decay index with height indicates that the region could produce a fast CME ($v >$ 1500~km~s$^{-1}$), which it did during events two and three. The AR's magnetic field environment, including sites of open magnetic field and null points along with the magnetic field connectivity and propagation direction of the CMEs play an important role in the escape and arrival of SEPs at Earth. Other SEP-productive ARs should be investigated to determine whether their magnetic field environment and CME propagation direction are significant in the escape and arrival of SEPs at Earth. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2208.12774v2-abstract-full').style.display = 'none'; document.getElementById('2208.12774v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 14 September, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 26 August, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Accepted in ApJ, 18 pages, 8 Figures, 2 Tables</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2205.05027">arXiv:2205.05027</a> <span> [<a href="https://arxiv.org/pdf/2205.05027">pdf</a>, <a href="https://arxiv.org/format/2205.05027">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/ac6e40">10.3847/1538-4357/ac6e40 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> What determines active region coronal plasma composition? </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Mihailescu%2C+T">Teodora Mihailescu</a>, <a href="/search/astro-ph?searchtype=author&query=Baker%2C+D">Deborah Baker</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">Lidia van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Long%2C+D+M">David M. Long</a>, <a href="/search/astro-ph?searchtype=author&query=Brooks%2C+D+H">David H. Brooks</a>, <a href="/search/astro-ph?searchtype=author&query=To%2C+A+S+H">Andy S. H. To</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2205.05027v1-abstract-short" style="display: inline;"> The chemical composition of the solar corona is different from that of the solar photosphere, with the strongest variation being observed in active regions (ARs). Using data from the Extreme Ultraviolet (EUV) Imaging Spectrometer (EIS) on Hinode, we present a survey of coronal elemental composition as expressed in the first ionisation potential (FIP) bias in 28 ARs of different ages and magnetic f… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2205.05027v1-abstract-full').style.display = 'inline'; document.getElementById('2205.05027v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2205.05027v1-abstract-full" style="display: none;"> The chemical composition of the solar corona is different from that of the solar photosphere, with the strongest variation being observed in active regions (ARs). Using data from the Extreme Ultraviolet (EUV) Imaging Spectrometer (EIS) on Hinode, we present a survey of coronal elemental composition as expressed in the first ionisation potential (FIP) bias in 28 ARs of different ages and magnetic flux content, which are at different stages in their evolution. We find no correlation between the FIP bias of an AR and its total unsigned magnetic flux or age. However, there is a weak dependence of FIP bias on the evolutionary stage, decreasing from 1.9-2.2 in ARs with spots to 1.5-1.6 in ARs that are at more advanced stages of the decay phase. FIP bias shows an increasing trend with average magnetic flux density up to 200 G but this trend does not continue at higher values. The FIP bias distribution within ARs has a spread between 0.4 and 1. The largest spread is observed in very dispersed ARs. We attribute this to a range of physical processes taking place in these ARs including processes associated with filament channel formation. These findings indicate that, while some general trends can be observed, the processes influencing the composition of an AR are complex and specific to its evolution, magnetic configuration or environment. The spread of FIP bias values in ARs shows a broad match with that previously observed in situ in the slow solar wind. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2205.05027v1-abstract-full').style.display = 'none'; document.getElementById('2205.05027v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 10 May, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">20 pages, 14 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2110.11714">arXiv:2110.11714</a> <span> [<a href="https://arxiv.org/pdf/2110.11714">pdf</a>, <a href="https://arxiv.org/format/2110.11714">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/ac32d2">10.3847/1538-4357/ac32d2 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Evolution of Plasma Composition in an Eruptive Flux Rope </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Baker%2C+D">Deborah Baker</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Brooks%2C+D+H">David H. Brooks</a>, <a href="/search/astro-ph?searchtype=author&query=D%C3%A9moulin%2C+P">Pascal D茅moulin</a>, <a href="/search/astro-ph?searchtype=author&query=van-Driel-Gesztelyi%2C+L">Lidia van-Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Mihailescu%2C+T">Teodora Mihailescu</a>, <a href="/search/astro-ph?searchtype=author&query=To%2C+A+S+H">Andy S. H. To</a>, <a href="/search/astro-ph?searchtype=author&query=Long%2C+D+M">David M. Long</a>, <a href="/search/astro-ph?searchtype=author&query=Yardley%2C+S+L">Stephanie L. Yardley</a>, <a href="/search/astro-ph?searchtype=author&query=Janvier%2C+M">Miho Janvier</a>, <a href="/search/astro-ph?searchtype=author&query=Valori%2C+G">Gherardo Valori</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2110.11714v1-abstract-short" style="display: inline;"> Magnetic flux ropes are bundles of twisted magnetic field enveloping a central axis. They harbor free magnetic energy and can be progenitors of coronal mass ejections (CMEs), but identifying flux ropes on the Sun can be challenging. One of the key coronal observables that has been shown to indicate the presence of a flux rope is a peculiar bright coronal structure called a sigmoid. In this work, w… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2110.11714v1-abstract-full').style.display = 'inline'; document.getElementById('2110.11714v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2110.11714v1-abstract-full" style="display: none;"> Magnetic flux ropes are bundles of twisted magnetic field enveloping a central axis. They harbor free magnetic energy and can be progenitors of coronal mass ejections (CMEs), but identifying flux ropes on the Sun can be challenging. One of the key coronal observables that has been shown to indicate the presence of a flux rope is a peculiar bright coronal structure called a sigmoid. In this work, we show Hinode EUV Imaging Spectrometer (EIS) observations of sigmoidal active region 10977. We analyze the coronal plasma composition in the active region and its evolution as the sigmoid (flux rope) forms and erupts as a CME. Plasma with photospheric composition was observed in coronal loops close to the main polarity inversion line during episodes of significant flux cancellation, suggestive of the injection of photospheric plasma into these loops driven by photospheric flux cancellation. Concurrently, the increasingly sheared core field contained plasma with coronal composition. As flux cancellation decreased and the sigmoid/flux rope formed, the plasma evolved to an intermediate composition in between photospheric and typical active region coronal compositions. Finally, the flux rope contained predominantly photospheric plasma during and after a failed eruption preceding the CME. The Hence, plasma composition observations of active region 10977 strongly support models of flux rope formation by photospheric flux cancellation forcing magnetic reconnection first at the photospheric level then at the coronal level. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2110.11714v1-abstract-full').style.display = 'none'; document.getElementById('2110.11714v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 22 October, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> October 2021. </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2106.16137">arXiv:2106.16137</a> <span> [<a href="https://arxiv.org/pdf/2106.16137">pdf</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1007/s11207-021-01849-7">10.1007/s11207-021-01849-7 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Plasma Upflows Induced by Magnetic Reconnection Above an Eruptive Flux Rope </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Baker%2C+D">Deborah Baker</a>, <a href="/search/astro-ph?searchtype=author&query=Mihailescu%2C+T">Teodora Mihailescu</a>, <a href="/search/astro-ph?searchtype=author&query=Demoulin%2C+P">Pascal Demoulin</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">Lidia van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Valori%2C+G">Gherardo Valori</a>, <a href="/search/astro-ph?searchtype=author&query=Brooks%2C+D+H">David H. Brooks</a>, <a href="/search/astro-ph?searchtype=author&query=Long%2C+D+M">David M. Long</a>, <a href="/search/astro-ph?searchtype=author&query=Janvier%2C+M">Miho Janvier</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2106.16137v1-abstract-short" style="display: inline;"> One of the major discoveries of Hinode's Extreme-ultraviolet Imaging Spectrometer (EIS) is the presence of upflows at the edges of active regions. As active regions are magnetically connected to the large-scale field of the corona, these upflows are a likely contributor to the global mass cycle in the corona. Here we examine the driving mechanism(s) of the very strong upflows with velocities in ex… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2106.16137v1-abstract-full').style.display = 'inline'; document.getElementById('2106.16137v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2106.16137v1-abstract-full" style="display: none;"> One of the major discoveries of Hinode's Extreme-ultraviolet Imaging Spectrometer (EIS) is the presence of upflows at the edges of active regions. As active regions are magnetically connected to the large-scale field of the corona, these upflows are a likely contributor to the global mass cycle in the corona. Here we examine the driving mechanism(s) of the very strong upflows with velocities in excess of 70 km/s, known as blue-wing asymmetries, observed during the eruption of a flux rope in AR 10977 (eruptive flare SOL2007-12-07T04:50). We use Hinode/EIS spectroscopic observations combined with magnetic-field modeling to investigate the possible link between the magnetic topology of the active region and the strong upflows. A Potential Field Source Surface (PFSS) extrapolation of the large-scale field shows a quadrupolar configuration with a separator lying above the flux rope. Field lines formed by induced reconnection along the separator before and during the flux-rope eruption are spatially linked to the strongest blue-wing asymmetries in the upflow regions. The flows are driven by the pressure gradient created when the dense and hot arcade loops of the active region reconnect with the extended and tenuous loops overlying it. In view of the fact that separator reconnection is a specific form of the more general quasi-separatrix (QSL) reconnection, we conclude that the mechanism driving the strongest upflows is, in fact, the same as the one driving the persistent upflows of approx. 10 - 20 km/s observed in all active regions. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2106.16137v1-abstract-full').style.display = 'none'; document.getElementById('2106.16137v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 30 June, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 2021. </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2104.04417">arXiv:2104.04417</a> <span> [<a href="https://arxiv.org/pdf/2104.04417">pdf</a>, <a href="https://arxiv.org/format/2104.04417">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Space Physics">physics.space-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1007/s11207-021-01861-x">10.1007/s11207-021-01861-x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Active region contributions to the solar wind over multiple solar cycles </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Stansby%2C+D">D. Stansby</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">L. van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Horbury%2C+T+S">T. S. Horbury</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2104.04417v2-abstract-short" style="display: inline;"> Both coronal holes and active regions are source regions of the solar wind. The distribution of these coronal structures across both space and time is well known, but it is unclear how much each source contributes to the solar wind. In this study we use photospheric magnetic field maps observed over the past four solar cycles to estimate what fraction of magnetic open solar flux is rooted in activ… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2104.04417v2-abstract-full').style.display = 'inline'; document.getElementById('2104.04417v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2104.04417v2-abstract-full" style="display: none;"> Both coronal holes and active regions are source regions of the solar wind. The distribution of these coronal structures across both space and time is well known, but it is unclear how much each source contributes to the solar wind. In this study we use photospheric magnetic field maps observed over the past four solar cycles to estimate what fraction of magnetic open solar flux is rooted in active regions, a proxy for the fraction of all solar wind originating in active regions. We find that the fractional contribution of active regions to the solar wind varies between 30% to 80% at any one time during solar maximum and is negligible at solar minimum, showing a strong correlation with sunspot number. While active regions are typically confined to latitudes $\pm$30$^{\circ}$ in the corona, the solar wind they produce can reach latitudes up to $\pm$60$^{\circ}$. Their fractional contribution to the solar wind also correlates with coronal mass ejection rate, and is highly variable, changing by $\pm$20% on monthly timescales within individual solar maxima. We speculate that these variations could be driven by coronal mass ejections causing reconfigurations of the coronal magnetic field on sub-monthly timescales. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2104.04417v2-abstract-full').style.display = 'none'; document.getElementById('2104.04417v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 10 August, 2021; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 9 April, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">18 pages, 7 figures. Published in Solar Physics</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Sol Phys 296, 116 (2021) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2103.17225">arXiv:2103.17225</a> <span> [<a href="https://arxiv.org/pdf/2103.17225">pdf</a>, <a href="https://arxiv.org/format/2103.17225">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1051/0004-6361/202140622">10.1051/0004-6361/202140622 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Solar origins of a strong stealth CME detected by Solar Orbiter </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=O%27Kane%2C+J">Jennifer O'Kane</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Davies%2C+E+E">Emma E. Davies</a>, <a href="/search/astro-ph?searchtype=author&query=M%C3%B6stl%2C+C">Christian M枚stl</a>, <a href="/search/astro-ph?searchtype=author&query=Hinterreiter%2C+J">J眉rgen Hinterreiter</a>, <a href="/search/astro-ph?searchtype=author&query=von+Forstner%2C+J+L+F">Johan L. Freiherr von Forstner</a>, <a href="/search/astro-ph?searchtype=author&query=Weiss%2C+A+J">Andreas J. Weiss</a>, <a href="/search/astro-ph?searchtype=author&query=Long%2C+D+M">David M. Long</a>, <a href="/search/astro-ph?searchtype=author&query=Amerstorfer%2C+T">Tanja Amerstorfer</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2103.17225v1-abstract-short" style="display: inline;"> Aims.We aim to locate the origin of a stealth coronal mass ejection (CME) detected in situ by the MAG instrument on board Solar Orbiter, and make connections between the CME observed at the Sun, and the interplanetary CME (ICME) measured in situ. Methods. Remote sensing data are analysed using advanced image processing techniques to identify the source region of the stealth CME, and the global mag… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2103.17225v1-abstract-full').style.display = 'inline'; document.getElementById('2103.17225v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2103.17225v1-abstract-full" style="display: none;"> Aims.We aim to locate the origin of a stealth coronal mass ejection (CME) detected in situ by the MAG instrument on board Solar Orbiter, and make connections between the CME observed at the Sun, and the interplanetary CME (ICME) measured in situ. Methods. Remote sensing data are analysed using advanced image processing techniques to identify the source region of the stealth CME, and the global magnetic field at the time of the eruption is examined using Potential Field Source Surface (PFSS) models. The observations of the stealth CME at the Sun are compared with the magnetic field measured by the Solar Orbiter spacecraft, and plasma properties measured by the Wind spacecraft. Results. The source of the CME is found to be a quiet Sun cavity in the northern hemisphere. We find that the stealth CME has a strong magnetic field in situ, despite originating from a quiet Sun region with an extremely weak magnetic field. Conclusions. The interaction of the ICME with its surrounding environment is the likely cause of a higher magnetic field strength measured in situ. Stealth CMEs require multi-wavelength and multi-viewpoint observations in order to confidently locate the source region, however their elusive signatures still pose many problems for space weather forecasting. The findings have implications for Solar Orbiter observing sequences with instruments such as EUI that are designed to capture stealth CMEs <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2103.17225v1-abstract-full').style.display = 'none'; document.getElementById('2103.17225v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 31 March, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">6 pages, 7 figures, accepted for publication in A&A</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2012.07708">arXiv:2012.07708</a> <span> [<a href="https://arxiv.org/pdf/2012.07708">pdf</a>, <a href="https://arxiv.org/format/2012.07708">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1007/s11207-020-01749-2">10.1007/s11207-020-01749-2 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Simulating the Coronal Evolution of Bipolar Active Regions to Investigate the Formation of Flux Ropes </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Yardley%2C+S+L">Stephanie L. Yardley</a>, <a href="/search/astro-ph?searchtype=author&query=Mackay%2C+D+H">Duncan H. Mackay</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2012.07708v1-abstract-short" style="display: inline;"> The coronal magnetic field evolution of 20 bipolar active regions (ARs) is simulated from their emergence to decay using the time-dependent nonlinear force-free field method of Mackay et al. A time sequence of cleaned photospheric line-of-sight magnetograms, that covers the entire evolution of each AR, is used to drive the simulation. A comparison of the simulated coronal magnetic field with the 1… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2012.07708v1-abstract-full').style.display = 'inline'; document.getElementById('2012.07708v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2012.07708v1-abstract-full" style="display: none;"> The coronal magnetic field evolution of 20 bipolar active regions (ARs) is simulated from their emergence to decay using the time-dependent nonlinear force-free field method of Mackay et al. A time sequence of cleaned photospheric line-of-sight magnetograms, that covers the entire evolution of each AR, is used to drive the simulation. A comparison of the simulated coronal magnetic field with the 171 and 193 A observations obtained by the Solar Dynamics Observatory (SDO)/ Atmospheric Imaging Assembly (AIA), is made for each AR by manual inspection. The results show that it is possible to reproduce the evolution of the main coronal features such as small- and large-scale coronal loops, filaments and sheared structures for 80% of the ARs. Varying the boundary and initial conditions, along with the addition of physical effects such as Ohmic diffusion, hyperdiffusion and a horizontal magnetic field injection at the photosphere, improves the match between the observations and simulated coronal evolution by 20%. The simulations were able to reproduce the build-up to eruption for 50% of the observed eruptions associated with the ARs. The mean unsigned time difference between the eruptions occurring in the observations compared to the time of eruption onset in the simulations was found to be ~5 hrs. The simulations were particularly successful in capturing the build-up to eruption for all four eruptions that originated from the internal polarity inversion line of the ARs. The technique was less successful in reproducing the onset of eruptions that originated from the periphery of ARs and large-scale coronal structures. For these cases global, rather than local, nonlinear force-free field models must be used. While the technique has shown some success, eruptions that occur in quick succession are difficult to reproduce by this method and future iterations of the model need to address this. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2012.07708v1-abstract-full').style.display = 'none'; document.getElementById('2012.07708v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 14 December, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">32 pages, 8 figures, accepted for publication</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2012.03757">arXiv:2012.03757</a> <span> [<a href="https://arxiv.org/pdf/2012.03757">pdf</a>, <a href="https://arxiv.org/format/2012.03757">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/abd2bf">10.3847/1538-4357/abd2bf <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The Magnetic Environment of a Stealth Coronal Mass Ejection </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=O%27Kane%2C+J">Jennifer O'Kane</a>, <a href="/search/astro-ph?searchtype=author&query=Mac+Cormack%2C+C">Cecilia Mac Cormack</a>, <a href="/search/astro-ph?searchtype=author&query=Mandrini%2C+C+H">Cristina H. Mandrini</a>, <a href="/search/astro-ph?searchtype=author&query=D%C3%A9moulin%2C+P">Pascal D茅moulin</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Long%2C+D+M">David M. Long</a>, <a href="/search/astro-ph?searchtype=author&query=Valori%2C+G">Gherardo Valori</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2012.03757v1-abstract-short" style="display: inline;"> Interest in stealth coronal mass ejections (CMEs) is increasing due to their relatively high occurrence rate and space weather impact. However, typical CME signatures such as extreme-ultraviolet dimmings and post-eruptive arcades are hard to identify and require extensive image processing techniques. These weak observational signatures mean that little is currently understood about the physics of… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2012.03757v1-abstract-full').style.display = 'inline'; document.getElementById('2012.03757v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2012.03757v1-abstract-full" style="display: none;"> Interest in stealth coronal mass ejections (CMEs) is increasing due to their relatively high occurrence rate and space weather impact. However, typical CME signatures such as extreme-ultraviolet dimmings and post-eruptive arcades are hard to identify and require extensive image processing techniques. These weak observational signatures mean that little is currently understood about the physics of these events. We present an extensive study of the magnetic field configuration in which the stealth CME of 3 March 2011 occurred. Three distinct episodes of flare ribbon formation are observed in the stealth CME source active region (AR). Two occurred prior to the eruption and suggest the occurrence of magnetic reconnection that builds the structure which will become eruptive. The third occurs in a time close to the eruption of a cavity that is observed in STEREO-B 171A data; this subsequently becomes part of the propagating CME observed in coronagraph data. We use both local (Cartesian) and global (spherical) models of the coronal magnetic field, which are complemented and verified by the observational analysis. We find evidence of a coronal null point, with field lines computed from its neighbourhood connecting the stealth CME source region to two ARs in the northern hemisphere. We conclude that reconnection at the null point aids the eruption of the stealth CME by removing field that acted to stabilise the pre-eruptive structure. This stealth CME, despite its weak signatures, has the main characteristics of other CMEs, and its eruption is driven by similar mechanisms. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2012.03757v1-abstract-full').style.display = 'none'; document.getElementById('2012.03757v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 7 December, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">15 pages, 12 figures, accepted for publication in The Astrophysical Journal</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2010.11204">arXiv:2010.11204</a> <span> [<a href="https://arxiv.org/pdf/2010.11204">pdf</a>, <a href="https://arxiv.org/format/2010.11204">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1051/0004-6361/202038781">10.1051/0004-6361/202038781 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> A new trigger mechanism for coronal mass ejections: the role of confined flares and photospheric motions in the formation of hot flux ropes </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=James%2C+A+W">Alexander W James</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M Green</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">Lidia van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Valori%2C+G">Gherardo Valori</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2010.11204v2-abstract-short" style="display: inline;"> Context: Many previous studies have shown that the magnetic precursor of a coronal mass ejection (CME) takes the form of a magnetic flux rope, and a subset of them have become known as `hot flux ropes' due to their emission signatures in $\sim$10 MK plasma. Aims: We seek to identify the processes by which these hot flux ropes form, with a view of developing our understanding of CMEs and thereby im… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2010.11204v2-abstract-full').style.display = 'inline'; document.getElementById('2010.11204v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2010.11204v2-abstract-full" style="display: none;"> Context: Many previous studies have shown that the magnetic precursor of a coronal mass ejection (CME) takes the form of a magnetic flux rope, and a subset of them have become known as `hot flux ropes' due to their emission signatures in $\sim$10 MK plasma. Aims: We seek to identify the processes by which these hot flux ropes form, with a view of developing our understanding of CMEs and thereby improving space weather forecasts. Methods: Extreme-ultraviolet observations were used to identify five pre-eruptive hot flux ropes in the solar corona and study how they evolved. Confined flares were observed in the hours and days before each flux rope erupted, and these were used as indicators of episodic bursts of magnetic reconnection by which each flux rope formed. The evolution of the photospheric magnetic field was observed during each formation period to identify the process(es) that enabled magnetic reconnection to occur in the $尾<1$ corona and form the flux ropes. Results: The confined flares were found to be homologous events and suggest flux rope formation times that range from 18 hours to 5 days. Throughout these periods, fragments of photospheric magnetic flux were observed to orbit around each other in sunspots where the flux ropes had a footpoint. Active regions with right-handed (left-handed) twisted magnetic flux exhibited clockwise (anticlockwise) orbiting motions, and right-handed (left-handed) flux ropes formed. Conclusions: We infer that the orbital motions of photospheric magnetic flux fragments about each other bring magnetic flux tubes together in the corona, enabling component reconnection that forms a magnetic flux rope above a flaring arcade. This represents a novel trigger mechanism for solar eruptions and should be considered when predicting solar magnetic activity. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2010.11204v2-abstract-full').style.display = 'none'; document.getElementById('2010.11204v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 11 December, 2020; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 21 October, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> October 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Accepted for publication in Astronomy & Astrophysics. 14 pages, 16 figures, 2 tables</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> A&A 644, A137 (2020) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2010.10186">arXiv:2010.10186</a> <span> [<a href="https://arxiv.org/pdf/2010.10186">pdf</a>, <a href="https://arxiv.org/format/2010.10186">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1007/s11214-020-00757-9">10.1007/s11214-020-00757-9 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Decoding the Pre-Eruptive Magnetic Field Configurations of Coronal Mass Ejections </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Patsourakos%2C+S">S. Patsourakos</a>, <a href="/search/astro-ph?searchtype=author&query=Vourlidas%2C+A">A. Vourlidas</a>, <a href="/search/astro-ph?searchtype=author&query=T%C3%B6r%C3%B6k%2C+T">T. T枚r枚k</a>, <a href="/search/astro-ph?searchtype=author&query=Kliem%2C+B">B. Kliem</a>, <a href="/search/astro-ph?searchtype=author&query=Antiochos%2C+S+K">S. K. Antiochos</a>, <a href="/search/astro-ph?searchtype=author&query=Archontis%2C+V">V. Archontis</a>, <a href="/search/astro-ph?searchtype=author&query=Aulanier%2C+G">G. Aulanier</a>, <a href="/search/astro-ph?searchtype=author&query=Cheng%2C+X">X. Cheng</a>, <a href="/search/astro-ph?searchtype=author&query=Chintzoglou%2C+G">G. Chintzoglou</a>, <a href="/search/astro-ph?searchtype=author&query=Georgoulis%2C+M+K">M. K. Georgoulis</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Leake%2C+J+E">J. E. Leake</a>, <a href="/search/astro-ph?searchtype=author&query=Moore%2C+R">R. Moore</a>, <a href="/search/astro-ph?searchtype=author&query=Nindos%2C+A">A. Nindos</a>, <a href="/search/astro-ph?searchtype=author&query=Syntelis%2C+P">P. Syntelis</a>, <a href="/search/astro-ph?searchtype=author&query=Yardley%2C+S+L">S. L. Yardley</a>, <a href="/search/astro-ph?searchtype=author&query=Yurchyshyn%2C+V">V. Yurchyshyn</a>, <a href="/search/astro-ph?searchtype=author&query=Zhang%2C+J">J. Zhang</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2010.10186v1-abstract-short" style="display: inline;"> A clear understanding of the nature of the pre-eruptive magnetic field configurations of Coronal Mass Ejections (CMEs) is required for understanding and eventually predicting solar eruptions. Only two, but seemingly disparate, magnetic configurations are considered viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes (MFR). They can form via three physical mechanisms (flux emerge… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2010.10186v1-abstract-full').style.display = 'inline'; document.getElementById('2010.10186v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2010.10186v1-abstract-full" style="display: none;"> A clear understanding of the nature of the pre-eruptive magnetic field configurations of Coronal Mass Ejections (CMEs) is required for understanding and eventually predicting solar eruptions. Only two, but seemingly disparate, magnetic configurations are considered viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes (MFR). They can form via three physical mechanisms (flux emergence, flux cancellation, helicity condensation) . Whether the CME culprit is an SMA or an MFR, however, has been strongly debated for thirty years. We formed an International Space Science Institute (ISSI) team to address and resolve this issue and report the outcome here. We review the status of the field across modeling and observations, identify the open and closed issues, compile lists of SMA and MFR observables to be tested against observations and outline research activities to close the gaps in our current understanding. We propose that the combination of multi-viewpoint multi-thermal coronal observations and multi-height vector magnetic field measurements is the optimal approach for resolving the issue conclusively. We demonstrate the approach using MHD simulations and synthetic coronal images. Our key conclusion is that the differentiation of pre-eruptive configurations in terms of SMAs and MFRs seems artificial. Both observations and modeling can be made consistent if the pre-eruptive configuration exists in a hybrid state that is continuously evolving from an SMA to an MFR. Thus, the 'dominant' nature of a given configuration will largely depend on its evolutionary stage (SMA-like early-on, MFR-like near the eruption). <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2010.10186v1-abstract-full').style.display = 'none'; document.getElementById('2010.10186v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 20 October, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> October 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Space Science Reviews, accepted for publication</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1911.01314">arXiv:1911.01314</a> <span> [<a href="https://arxiv.org/pdf/1911.01314">pdf</a>, <a href="https://arxiv.org/format/1911.01314">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/ab54d2">10.3847/1538-4357/ab54d2 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Understanding the plasma and magnetic field evolution of a filament using observations and Nonlinear force-free field modelling </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Yardley%2C+S+L">Stephanie L. Yardley</a>, <a href="/search/astro-ph?searchtype=author&query=Savcheva%2C+A">Antonia Savcheva</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">Lidia van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Long%2C+D">David Long</a>, <a href="/search/astro-ph?searchtype=author&query=Williams%2C+D+R">David R. Williams</a>, <a href="/search/astro-ph?searchtype=author&query=Mackay%2C+D+H">Duncan H. Mackay</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1911.01314v1-abstract-short" style="display: inline;"> We present observations and magnetic field models of an intermediate filament present on the Sun in August 2012, associated with a polarity inversion line that extends from AR 11541 in the east into the quiet sun at its western end. A combination of SDO/AIA, SDO/HMI, and GONG H alpha data allow us to analyse the structure and evolution of the filament from 2012 August 4 23:00 UT to 2012 August 6 0… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1911.01314v1-abstract-full').style.display = 'inline'; document.getElementById('1911.01314v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1911.01314v1-abstract-full" style="display: none;"> We present observations and magnetic field models of an intermediate filament present on the Sun in August 2012, associated with a polarity inversion line that extends from AR 11541 in the east into the quiet sun at its western end. A combination of SDO/AIA, SDO/HMI, and GONG H alpha data allow us to analyse the structure and evolution of the filament from 2012 August 4 23:00 UT to 2012 August 6 08:00 UT when the filament was in equilibrium. By applying the flux rope insertion method, nonlinear force-free field models of the filament are constructed using SDO/HMI line-of-sight magnetograms as the boundary condition at the two times given above. Guided by observed filament barbs, both modelled flux ropes are split into three sections each with a different value of axial flux to represent the non-uniform photospheric field distribution. The flux in the eastern section of the rope increases by 4$\times$10$^{20}$ Mx between the two models, which is in good agreement with the amount of flux cancelled along the internal PIL of AR 11541, calculated to be 3.2$\times$10$^{20}$ Mx. This suggests that flux cancellation builds flux into the filament's magnetic structure. Additionally, the number of field line dips increases between the two models in the locations where flux cancellation, the formation of new filament threads and growth of the filament is observed. This suggests that flux cancellation associated with magnetic reconnection forms concave-up magnetic field that lifts plasma into the filament. During this time, the free magnetic energy in the models increases by 0.2$\times$10$^{31}$ ergs. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1911.01314v1-abstract-full').style.display = 'none'; document.getElementById('1911.01314v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 4 November, 2019; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2019. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">17 pages, 10 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1902.06948">arXiv:1902.06948</a> <span> [<a href="https://arxiv.org/pdf/1902.06948">pdf</a>, <a href="https://arxiv.org/format/1902.06948">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/ab07c1">10.3847/1538-4357/ab07c1 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Transient Inverse-FIP Plasma Composition Evolution within a Confined Solar Flare </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Baker%2C+D">Deborah Baker</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">Lidia van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Brooks%2C+D+H">David H. Brooks</a>, <a href="/search/astro-ph?searchtype=author&query=Valori%2C+G">Gherardo Valori</a>, <a href="/search/astro-ph?searchtype=author&query=James%2C+A+W">Alexander W. James</a>, <a href="/search/astro-ph?searchtype=author&query=Laming%2C+J+M">J. Martin Laming</a>, <a href="/search/astro-ph?searchtype=author&query=Long%2C+D+M">David M. Long</a>, <a href="/search/astro-ph?searchtype=author&query=Demoulin%2C+P">Pascal Demoulin</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Matthews%2C+S+A">Sarah A. Matthews</a>, <a href="/search/astro-ph?searchtype=author&query=Olah%2C+K">Katalin Olah</a>, <a href="/search/astro-ph?searchtype=author&query=Kovari%2C+Z">Zsolt Kovari</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1902.06948v1-abstract-short" style="display: inline;"> Understanding elemental abundance variations in the solar corona provides an insight into how matter and energy flow from the chromosphere into the heliosphere. Observed variations depend on the first ionization potential (FIP) of the main elements of the Sun's atmosphere. High-FIP elements (>10 eV) maintain photospheric abundances in the corona, whereas low-FIP elements have enhanced abundances.… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1902.06948v1-abstract-full').style.display = 'inline'; document.getElementById('1902.06948v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1902.06948v1-abstract-full" style="display: none;"> Understanding elemental abundance variations in the solar corona provides an insight into how matter and energy flow from the chromosphere into the heliosphere. Observed variations depend on the first ionization potential (FIP) of the main elements of the Sun's atmosphere. High-FIP elements (>10 eV) maintain photospheric abundances in the corona, whereas low-FIP elements have enhanced abundances. Conversely, inverse FIP (IFIP) refers to the enhancement of high-FIP or depletion of low-FIP elements. We use spatially resolved spectroscopic observations, specifically the Ar XIV/Ca XIV intensity ratio, from Hinode's Extreme-ultraviolet Imaging Spectrometer to investigate the distribution and evolution of plasma composition within two confined flares in a newly emerging, highly sheared active region. During the decay phase of the first flare, patches above the flare ribbons evolve from the FIP to the IFIP effect, while the flaring loop tops show a stronger FIP effect. The patch and loop compositions then evolve toward the pre-flare basal state. We propose an explanation of how flaring in strands of highly sheared emerging magnetic fields can lead to flare-modulated IFIP plasma composition over coalescing umbrae which are crossed by flare ribbons. Subsurface reconnection between the coalescing umbrae leads to the depletion of low-FIP elements as a result of an increased wave flux from below. This material is evaporated when the flare ribbons cross the umbrae. Our results are consistent with the ponderomotive fractionation model (Laming2015) for the creation of IFIP-biased plasma. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1902.06948v1-abstract-full').style.display = 'none'; document.getElementById('1902.06948v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 19 February, 2019; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 2019. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">18 pages, 9 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1808.10635">arXiv:1808.10635</a> <span> [<a href="https://arxiv.org/pdf/1808.10635">pdf</a>, <a href="https://arxiv.org/format/1808.10635">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/aade4a">10.3847/1538-4357/aade4a <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The role of flux cancellation in eruptions from bipolar active regions </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Yardley%2C+S+L">S. L. Yardley</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Van+Driel-Gesztelyi%2C+L">L. Van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Williams%2C+D+R">D. R. Williams</a>, <a href="/search/astro-ph?searchtype=author&query=Mackay%2C+D+H">D. H. Mackay</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1808.10635v1-abstract-short" style="display: inline;"> The physical processes or trigger mechanisms that lead to the eruption of coronal mass ejections (CMEs), the largest eruptive phenomenon in the heliosphere, are still undetermined. Low-altitude magnetic reconnection associated with flux cancellation appears to play an important role in CME occurrence as it can form an eruptive configuration and reduce the magnetic flux that contributes to the over… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1808.10635v1-abstract-full').style.display = 'inline'; document.getElementById('1808.10635v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1808.10635v1-abstract-full" style="display: none;"> The physical processes or trigger mechanisms that lead to the eruption of coronal mass ejections (CMEs), the largest eruptive phenomenon in the heliosphere, are still undetermined. Low-altitude magnetic reconnection associated with flux cancellation appears to play an important role in CME occurrence as it can form an eruptive configuration and reduce the magnetic flux that contributes to the overlying, stabilising field. We conduct the first comprehensive study of 20 small bipolar active regions in order to probe the role of flux cancellation as an eruption trigger mechanism. We categorise eruptions from the bipolar regions into three types related to location and find that the type of eruption produced depends on the evolutionary stage of the active region. In addition we find that active regions that form eruptive structures by flux cancellation (low-altitude reconnection) had, on average, lower flux cancellation rates than the active region sample as a whole. Therefore, while flux cancellation plays a key role, by itself it is insufficient for the production of an eruption. The results support that although flux cancellation in a sheared arcade may be able to build an eruptive configuration, a successful eruption depends upon the removal of sufficient overlying and stabilising field. Convergence of the bipole polarities also appears to be present in regions that produce an eruption. These findings have important implications for understanding the physical processes that occur on our Sun in relation to CMEs and for space weather forecasting. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1808.10635v1-abstract-full').style.display = 'none'; document.getElementById('1808.10635v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 31 August, 2018; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2018. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">16 pages, 4 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1803.04769">arXiv:1803.04769</a> <span> [<a href="https://arxiv.org/pdf/1803.04769">pdf</a>, <a href="https://arxiv.org/format/1803.04769">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1002/2017SW001767">10.1002/2017SW001767 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Coronal Magnetic Structure of Earthbound CMEs and In situ Comparison </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Palmerio%2C+E">Erika Palmerio</a>, <a href="/search/astro-ph?searchtype=author&query=Kilpua%2C+E+K+J">Emilia K. J. Kilpua</a>, <a href="/search/astro-ph?searchtype=author&query=M%C3%B6stl%2C+C">Christian M枚stl</a>, <a href="/search/astro-ph?searchtype=author&query=Bothmer%2C+V">Volker Bothmer</a>, <a href="/search/astro-ph?searchtype=author&query=James%2C+A+W">Alexander W. James</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Isavnin%2C+A">Alexey Isavnin</a>, <a href="/search/astro-ph?searchtype=author&query=Davies%2C+J+A">Jackie A. Davies</a>, <a href="/search/astro-ph?searchtype=author&query=Harrison%2C+R+A">Richard A. Harrison</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1803.04769v2-abstract-short" style="display: inline;"> Predicting the magnetic field within an Earth-directed coronal mass ejection (CME) well before its arrival at Earth is one of the most important issues in space weather research. In this article, we compare the intrinsic flux rope type, i.e. the CME orientation and handedness during eruption, with the in situ flux rope type for 20 CME events that have been uniquely linked from Sun to Earth through… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1803.04769v2-abstract-full').style.display = 'inline'; document.getElementById('1803.04769v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1803.04769v2-abstract-full" style="display: none;"> Predicting the magnetic field within an Earth-directed coronal mass ejection (CME) well before its arrival at Earth is one of the most important issues in space weather research. In this article, we compare the intrinsic flux rope type, i.e. the CME orientation and handedness during eruption, with the in situ flux rope type for 20 CME events that have been uniquely linked from Sun to Earth through heliospheric imaging. Our study shows that the intrinsic flux rope type can be estimated for CMEs originating from different source regions using a combination of indirect proxies. We find that only 20% of the events studied match strictly between the intrinsic and in situ flux rope types. The percentage rises to 55% when intermediate cases (where the orientation at the Sun and/or in situ is close to 45掳) are considered as a match. We also determine the change in the flux rope tilt angle between the Sun and Earth. For the majority of the cases, the rotation is several tens of degrees, whilst 35% of the events change by more than 90掳. While occasionally the intrinsic flux rope type is a good proxy for the magnetic structure impacting Earth, our study highlights the importance of capturing the CME evolution for space weather forecasting purposes. Moreover, we emphasize that determination of the intrinsic flux rope type is a crucial input for CME forecasting models. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1803.04769v2-abstract-full').style.display = 'none'; document.getElementById('1803.04769v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 26 March, 2018; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 13 March, 2018; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2018. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">27 pages, 6 figures, accepted for publication in Space Weather</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1802.07965">arXiv:1802.07965</a> <span> [<a href="https://arxiv.org/pdf/1802.07965">pdf</a>, <a href="https://arxiv.org/format/1802.07965">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/2041-8213/aab15d">10.3847/2041-8213/aab15d <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> An Observationally-Constrained Model of a Flux Rope that Formed in the Solar Corona </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=James%2C+A+W">Alexander W. James</a>, <a href="/search/astro-ph?searchtype=author&query=Valori%2C+G">Gherardo Valori</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Liu%2C+Y">Yang Liu</a>, <a href="/search/astro-ph?searchtype=author&query=Cheung%2C+M+C+M">Mark C. M. Cheung</a>, <a href="/search/astro-ph?searchtype=author&query=Guo%2C+Y">Yang Guo</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">Lidia van Driel-Gesztelyi</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1802.07965v1-abstract-short" style="display: inline;"> Coronal mass ejections (CMEs) are large-scale eruptions of plasma from the coronae of stars. Understanding the plasma processes involved in CME initiation has applications to space weather forecasting and laboratory plasma experiments. James et al. (Sol. Phys. 292, 71, 2017) used EUV observations to conclude that a magnetic flux rope formed in the solar corona above NOAA Active Region 11504 before… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1802.07965v1-abstract-full').style.display = 'inline'; document.getElementById('1802.07965v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1802.07965v1-abstract-full" style="display: none;"> Coronal mass ejections (CMEs) are large-scale eruptions of plasma from the coronae of stars. Understanding the plasma processes involved in CME initiation has applications to space weather forecasting and laboratory plasma experiments. James et al. (Sol. Phys. 292, 71, 2017) used EUV observations to conclude that a magnetic flux rope formed in the solar corona above NOAA Active Region 11504 before it erupted on 14 June 2012 (SOL2012-06-14). In this work, we use data from the Solar Dynamics Observatory to model the coronal magnetic field of the active region one hour prior to eruption using a nonlinear force-free field extrapolation, and find a flux rope reaching a maximum height of 150 Mm above the photosphere. Estimations of the average twist of the strongly asymmetric extrapolated flux rope are between 1.35 and 1.88 turns, depending on the choice of axis, although the erupting structure was not observed to kink. The decay index near the apex of the axis of the extrapolated flux rope is comparable to typical critical values required for the onset of the torus instability, so we suggest that the torus instability drove the eruption. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1802.07965v1-abstract-full').style.display = 'none'; document.getElementById('1802.07965v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 22 February, 2018; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 2018. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">8 pages, 5 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1712.00396">arXiv:1712.00396</a> <span> [<a href="https://arxiv.org/pdf/1712.00396">pdf</a>, <a href="https://arxiv.org/format/1712.00396">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Space Physics">physics.space-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/aa9f20">10.3847/1538-4357/aa9f20 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Simulating the Coronal Evolution of AR 11437 using SDO/HMI Magnetograms </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Yardley%2C+S+L">Stephanie L. Yardley</a>, <a href="/search/astro-ph?searchtype=author&query=Mackay%2C+D+H">Duncan H. Mackay</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1712.00396v1-abstract-short" style="display: inline;"> The coronal magnetic field evolution of AR 11437 is simulated by applying the magnetofrictional relaxation technique of Mackay et al. (2011). A sequence of photospheric line-of-sight magnetograms produced by SDO/HMI are used to drive the simulation and continuously evolve the coronal magnetic field of the active region through a series of non-linear force-free equilibria. The simulation is started… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1712.00396v1-abstract-full').style.display = 'inline'; document.getElementById('1712.00396v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1712.00396v1-abstract-full" style="display: none;"> The coronal magnetic field evolution of AR 11437 is simulated by applying the magnetofrictional relaxation technique of Mackay et al. (2011). A sequence of photospheric line-of-sight magnetograms produced by SDO/HMI are used to drive the simulation and continuously evolve the coronal magnetic field of the active region through a series of non-linear force-free equilibria. The simulation is started during the first stages of the active region emergence so that its full evolution from emergence to decay can be simulated. A comparison of the simulation results with SDO/AIA observations show that many aspects of the active region's observed coronal evolution are reproduced. In particular, it shows the presence of a flux rope, which forms at the same location as sheared coronal loops in the observations. The observations show that eruptions occur on 2012 March 17 at 05:09 UT and 10:45 UT and on 2012 March 20 at 14:31 UT. The simulation reproduces the first and third eruption, with the simulated flux rope erupting roughly 1 and 10 hours before the observed ejections, respectively. A parameter study is conducted where the boundary and initial conditions are varied along with the physical effects of Ohmic diffusion, hyperdiffusion and an additional injection of helicity. When comparing the simulations, the evolution of the magnetic field, free magnetic energy, relative helicity and flux rope eruption timings do not change significantly. This indicates that the key element in reproducing the coronal evolution of AR 11437 is the use of line-of-sight magnetograms to drive the evolution of the coronal magnetic field. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1712.00396v1-abstract-full').style.display = 'none'; document.getElementById('1712.00396v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 1 December, 2017; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2017. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">18 pages, 13 figures, accepted in ApJ</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1709.04874">arXiv:1709.04874</a> <span> [<a href="https://arxiv.org/pdf/1709.04874">pdf</a>, <a href="https://arxiv.org/format/1709.04874">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/aa8db6">10.3847/1538-4357/aa8db6 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The 17 February 2013 sunquake in the context of the active region's magnetic field configuration </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Valori%2C+G">Gherardo Valori</a>, <a href="/search/astro-ph?searchtype=author&query=Zuccarello%2C+F+P">Francesco P. Zuccarello</a>, <a href="/search/astro-ph?searchtype=author&query=Zharkov%2C+S">Sergei Zharkov</a>, <a href="/search/astro-ph?searchtype=author&query=Matthews%2C+S">Sarah Matthews</a>, <a href="/search/astro-ph?searchtype=author&query=Guglielmino%2C+S+L">Salvo L. Guglielmino</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1709.04874v1-abstract-short" style="display: inline;"> Sunquakes are created by the hydrodynamic response of the lower atmosphere to a sudden deposition of energy and momentum. In this study we investigate a sunquake that occurred in NOAA active region 11675 on 17 February 2013. Observations of the corona, chromosphere and photosphere are brought together for the first time with a non-linear force-free model of the active region's magnetic field in or… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1709.04874v1-abstract-full').style.display = 'inline'; document.getElementById('1709.04874v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1709.04874v1-abstract-full" style="display: none;"> Sunquakes are created by the hydrodynamic response of the lower atmosphere to a sudden deposition of energy and momentum. In this study we investigate a sunquake that occurred in NOAA active region 11675 on 17 February 2013. Observations of the corona, chromosphere and photosphere are brought together for the first time with a non-linear force-free model of the active region's magnetic field in order to probe the magnetic environment in which the sunquake was initiated. We find that the sunquake was associated with the destabilization of a flux rope and an associated M-class GOES flare. Active region 11675 was in its emergence phase at the time of the sunquake and photospheric motions caused by the emergence heavily modified the flux rope and its associated quasi-separatrix layers, eventually triggering the flux rope's instability. The flux rope was surrounded by an extended envelope of field lines rooted in a small area at the approximate position of the sunquake. We argue that the configuration of the envelope, by interacting with the expanding flux rope, created a "magnetic lens" that may have focussed energy in one particular location the photosphere, creating the necessary conditions for the initiation of the sunquake. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1709.04874v1-abstract-full').style.display = 'none'; document.getElementById('1709.04874v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 14 September, 2017; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2017. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">20 pages, 16 Figures. Some figures have lower resolution than published version</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1703.10837">arXiv:1703.10837</a> <span> [<a href="https://arxiv.org/pdf/1703.10837">pdf</a>, <a href="https://arxiv.org/format/1703.10837">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1007/s11207-017-1093-4">10.1007/s11207-017-1093-4 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> On-disc Observations of Flux Rope Formation Prior to its Eruption </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=James%2C+A+W">A. W. James</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Palmerio%2C+E">E. Palmerio</a>, <a href="/search/astro-ph?searchtype=author&query=Valori%2C+G">G. Valori</a>, <a href="/search/astro-ph?searchtype=author&query=Reid%2C+H+A+S">H. A. S. Reid</a>, <a href="/search/astro-ph?searchtype=author&query=Baker%2C+D">D. Baker</a>, <a href="/search/astro-ph?searchtype=author&query=Brooks%2C+D+H">D. H. Brooks</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">L. van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Kilpua%2C+E+K+J">E. K. J. Kilpua</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1703.10837v1-abstract-short" style="display: inline;"> Coronal mass ejections (CMEs) are one of the primary manifestations of solar activity and can drive severe space weather effects. Therefore, it is vital to work towards being able to predict their occurrence. However, many aspects of CME formation and eruption remain unclear, including whether magnetic flux ropes are present before the onset of eruption and the key mechanisms that cause CMEs to oc… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1703.10837v1-abstract-full').style.display = 'inline'; document.getElementById('1703.10837v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1703.10837v1-abstract-full" style="display: none;"> Coronal mass ejections (CMEs) are one of the primary manifestations of solar activity and can drive severe space weather effects. Therefore, it is vital to work towards being able to predict their occurrence. However, many aspects of CME formation and eruption remain unclear, including whether magnetic flux ropes are present before the onset of eruption and the key mechanisms that cause CMEs to occur. In this work, the pre-eruptive coronal configuration of an active region that produced an interplanetary CME with a clear magnetic flux rope structure at 1 AU is studied. A forward-S sigmoid appears in extreme-ultraviolet (EUV) data two hours before the onset of the eruption (SOL2012-06-14), which is interpreted as a signature of a right-handed flux rope that formed prior to the eruption. Flare ribbons and EUV dimmings are used to infer the locations of the flux rope footpoints. These locations, together with observations of the global magnetic flux distribution, indicate that an interaction between newly emerged magnetic flux and pre-existing sunspot field in the days prior to the eruption may have enabled the coronal flux rope to form via tether-cutting-like reconnection. Composition analysis suggests that the flux rope had a coronal plasma composition, supporting our interpretation that the flux rope formed via magnetic reconnection in the corona. Once formed, the flux rope remained stable for 2 hours before erupting as a CME. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1703.10837v1-abstract-full').style.display = 'none'; document.getElementById('1703.10837v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 31 March, 2017; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2017. </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1701.08595">arXiv:1701.08595</a> <span> [<a href="https://arxiv.org/pdf/1701.08595">pdf</a>, <a href="https://arxiv.org/format/1701.08595">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1007/s11207-017-1063-x">10.1007/s11207-017-1063-x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Determining the Intrinsic CME Flux Rope Type Using Remote-sensing Solar Disk Observations </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Palmerio%2C+E">Erika Palmerio</a>, <a href="/search/astro-ph?searchtype=author&query=Kilpua%2C+E+K+J">Emilia K. J. Kilpua</a>, <a href="/search/astro-ph?searchtype=author&query=James%2C+A+W">Alexander W. James</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Pomoell%2C+J">Jens Pomoell</a>, <a href="/search/astro-ph?searchtype=author&query=Isavnin%2C+A">Alexey Isavnin</a>, <a href="/search/astro-ph?searchtype=author&query=Valori%2C+G">Gherardo Valori</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1701.08595v1-abstract-short" style="display: inline;"> A key aim in space weather research is to be able to use remote-sensing observations of the solar atmosphere to extend the lead time of predicting the geoeffectiveness of a coronal mass ejection (CME). In order to achieve this, the magnetic structure of the CME as it leaves the Sun must be known. In this article we address this issue by developing a method to determine the intrinsic flux rope type… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1701.08595v1-abstract-full').style.display = 'inline'; document.getElementById('1701.08595v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1701.08595v1-abstract-full" style="display: none;"> A key aim in space weather research is to be able to use remote-sensing observations of the solar atmosphere to extend the lead time of predicting the geoeffectiveness of a coronal mass ejection (CME). In order to achieve this, the magnetic structure of the CME as it leaves the Sun must be known. In this article we address this issue by developing a method to determine the intrinsic flux rope type of a CME solely from solar disk observations. We use several well known proxies for the magnetic helicity sign, the axis orientation, and the axial magnetic field direction to predict the magnetic structure of the interplanetary flux rope. We present two case studies: the 2 June 2011 and the 14 June 2012 CMEs. Both of these events erupted from an active region and, despite having clear in situ counterparts, their eruption characteristics were relatively complex. The first event was associated with an active region filament that erupted in two stages, while for the other event the eruption originated from a relatively high coronal altitude and the source region did not feature the presence of a filament. Our magnetic helicity sign proxies include the analysis of magnetic tongues, soft X-ray and/or EUV sigmoids, coronal arcade skew, filament emission and absorption threads, and filament rotation. Since the inclination of the post-eruption arcades was not clear, we use the tilt of the polarity inversion line to determine the flux rope axis orientation, and coronal dimmings to determine the flux rope footpoints and, therefore, the direction of the axial magnetic field. The comparison of the estimated intrinsic flux rope structure to in situ observations at the Lagrangian point L1 indicated a good agreement with the predictions. Our results highlight the flux rope type determination techniques that are particularly useful for active region eruptions, where most geoeffective CMEs originate. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1701.08595v1-abstract-full').style.display = 'none'; document.getElementById('1701.08595v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 30 January, 2017; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> January 2017. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">24 pages, 7 figures, accepted for publication in Solar Physics</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Solar Phys., 292:39, 2017 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1606.08264">arXiv:1606.08264</a> <span> [<a href="https://arxiv.org/pdf/1606.08264">pdf</a>, <a href="https://arxiv.org/format/1606.08264">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/0004-637X/827/2/151">10.3847/0004-637X/827/2/151 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Flux cancellation and the evolution of the eruptive filament of 2011 June 7 </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Yardley%2C+S+L">S. L. Yardley</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Williams%2C+D+R">D. R. Williams</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">L. van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Valori%2C+G">G. Valori</a>, <a href="/search/astro-ph?searchtype=author&query=Dacie%2C+S">S. Dacie</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1606.08264v1-abstract-short" style="display: inline;"> We investigate whether flux cancellation is responsible for the formation of a very massive filament resulting in the spectacular 2011 June 7 eruption. We analyse and quantify the amount of flux cancellation that occurs in NOAA AR 11226 and its two neighbouring ARs (11227 & 11233) using line-of-sight magnetograms from the Heliospheric Magnetic Imager. During a 3.6-day period building up to the fil… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1606.08264v1-abstract-full').style.display = 'inline'; document.getElementById('1606.08264v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1606.08264v1-abstract-full" style="display: none;"> We investigate whether flux cancellation is responsible for the formation of a very massive filament resulting in the spectacular 2011 June 7 eruption. We analyse and quantify the amount of flux cancellation that occurs in NOAA AR 11226 and its two neighbouring ARs (11227 & 11233) using line-of-sight magnetograms from the Heliospheric Magnetic Imager. During a 3.6-day period building up to the filament eruption, 1.7 x 10^21 Mx, 21% of AR 11226's maximum magnetic flux, was cancelled along the polarity inversion line (PIL) where the filament formed. If the flux cancellation continued at the same rate up until the eruption then up to 2.8 x 10^21 Mx (34% of the AR flux) may have been built into the magnetic configuration that contains the filament plasma. The large flux cancellation rate is due to an unusual motion of the positive polarity sunspot, which splits, with the largest section moving rapidly towards the PIL. This motion compresses the negative polarity and leads to the formation of an orphan penumbra where one end of the filament is rooted. Dense plasma threads above the orphan penumbra build into the filament, extending its length, and presumably injecting material into it. We conclude that the exceptionally strong flux cancellation in AR 11226 played a significant role in the formation of its unusually massive filament. In addition, the presence and coherent evolution of bald patches in the vector magnetic field along the PIL suggests that the magnetic field configuration supporting the filament material is that of a flux rope. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1606.08264v1-abstract-full').style.display = 'none'; document.getElementById('1606.08264v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 27 June, 2016; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 2016. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">18 pages, 7 figures. Submitted to ApJ in December 2015, accepted in June 2016</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1508.07216">arXiv:1508.07216</a> <span> [<a href="https://arxiv.org/pdf/1508.07216">pdf</a>, <a href="https://arxiv.org/ps/1508.07216">ps</a>, <a href="https://arxiv.org/format/1508.07216">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/0004-637X/812/1/35">10.1088/0004-637X/812/1/35 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Spectroscopic Signatures Related to a Sunquake </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Matthews%2C+S+A">Sarah A. Matthews</a>, <a href="/search/astro-ph?searchtype=author&query=Harra%2C+L+K">Louise K. Harra</a>, <a href="/search/astro-ph?searchtype=author&query=Zharkov%2C+S">Sergei Zharkov</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1508.07216v1-abstract-short" style="display: inline;"> The presence of flare related acoustic emission (sunquakes) in some flares represents a severe challenge to our current understanding of flare energy transport processes. We present a comparison of new spectral observations from Hinode's EUV imaging Spectrometer (EIS) and the Interface Region Imaging Spectrograph (IRIS) of the atmosphere above a sunquake, and compare them to the spectra observed i… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1508.07216v1-abstract-full').style.display = 'inline'; document.getElementById('1508.07216v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1508.07216v1-abstract-full" style="display: none;"> The presence of flare related acoustic emission (sunquakes) in some flares represents a severe challenge to our current understanding of flare energy transport processes. We present a comparison of new spectral observations from Hinode's EUV imaging Spectrometer (EIS) and the Interface Region Imaging Spectrograph (IRIS) of the atmosphere above a sunquake, and compare them to the spectra observed in a part of the flaring region with no acoustic signature. Evidence for the sunquake is determined using both time-distance and acoustic holography methods, and we find that, unlike many previous sunquake detections, the signal is rather dispersed, but that the time-distance and 6 and 7 mHz sources converge at the same spatial location. We also see some evidence for different evolution at different frequencies, with an earlier peak at 7 mHz than at 6 mHz. Using spectroscopic measurements we find that in this location at the time of the 7 mHz peak the spectral emission is significantly more intense, shows larger velocity shifts and substantially broader profiles than in the location with no sunquake, and that there is a good correlation between blue-shifted, hot coronal, hard X-ray (HXR) and red-shifted chromospheric emission, consistent with the idea of a strong downward motion driven by rapid heating by non-thermal electrons and the formation of chromospheric shocks. Exploiting the diagnostic potential of the Mg II triplet lines, we also find evidence for a single, large temperature increase deep in the atmosphere, consistent with this scenario. The time of the 6 mHz and time-distance peak signal coincides with a secondary peak in the energy release process, but in this case we find no evidence of HXR emission in the quake location, but very broad spectral lines, strongly shifted to the red, indicating the possible presence of a significant flux of downward propagating Alfven waves. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1508.07216v1-abstract-full').style.display = 'none'; document.getElementById('1508.07216v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 28 August, 2015; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2015. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">39 pages, 13 figures, accepted for publication in ApJ</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1501.07397">arXiv:1501.07397</a> <span> [<a href="https://arxiv.org/pdf/1501.07397">pdf</a>, <a href="https://arxiv.org/format/1501.07397">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/0004-637X/802/2/104">10.1088/0004-637X/802/2/104 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> FIP Bias Evolution in a Decaying Active Region </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Baker%2C+D">D. Baker</a>, <a href="/search/astro-ph?searchtype=author&query=Brooks%2C+D+H">D. H. Brooks</a>, <a href="/search/astro-ph?searchtype=author&query=D%C3%A9moulin%2C+P">P. D茅moulin</a>, <a href="/search/astro-ph?searchtype=author&query=Yardley%2C+S+L">S. L. Yardley</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">L. van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Long%2C+D+M">D. M. Long</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1501.07397v1-abstract-short" style="display: inline;"> Solar coronal plasma composition is typically characterized by first ionization potential (FIP) bias. Using spectra obtained by Hinode's EUV Imaging Spectrometer (EIS) instrument, we present a series of large-scale, spatially resolved composition maps of active region (AR) 11389. The composition maps show how FIP bias evolves within the decaying AR from 2012 January 4-6. Globally, FIP bias decreas… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1501.07397v1-abstract-full').style.display = 'inline'; document.getElementById('1501.07397v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1501.07397v1-abstract-full" style="display: none;"> Solar coronal plasma composition is typically characterized by first ionization potential (FIP) bias. Using spectra obtained by Hinode's EUV Imaging Spectrometer (EIS) instrument, we present a series of large-scale, spatially resolved composition maps of active region (AR) 11389. The composition maps show how FIP bias evolves within the decaying AR from 2012 January 4-6. Globally, FIP bias decreases throughout the AR. We analyzed areas of significant plasma composition changes within the decaying AR and found that small-scale evolution in the photospheric magnetic field is closely linked to the FIP bias evolution observed in the corona. During the AR's decay phase, small bipoles emerging within supergranular cells reconnect with the pre-existing AR field, creating a pathway along which photospheric and coronal plasmas can mix. The mixing time scales are shorter than those of plasma enrichment processes. Eruptive activity also results in shifting the FIP bias closer to photospheric in the affected areas. Finally, the FIP bias still remains dominantly coronal only in a part of the AR's high-flux density core. We conclude that in the decay phase of an AR's lifetime, the FIP bias is becoming increasingly modulated by episodes of small-scale flux emergence, i.e. decreasing the AR's overall FIP bias. Our results show that magnetic field evolution plays an important role in compositional changes during AR development, revealing a more complex relationship than expected from previous well-known Skylab results showing that FIP bias increases almost linearly with age in young ARs (Widing $\&$ Feldman, 2001, ApJ, 555, 426). <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1501.07397v1-abstract-full').style.display = 'none'; document.getElementById('1501.07397v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 29 January, 2015; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> January 2015. </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1412.5623">arXiv:1412.5623</a> <span> [<a href="https://arxiv.org/pdf/1412.5623">pdf</a>, <a href="https://arxiv.org/format/1412.5623">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1007/s11207-014-0646-z">10.1007/s11207-014-0646-z <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Atmospheric Response to of an Active Region to new Small Flux Emergence </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Shelton%2C+D+L">D. L. Shelton</a>, <a href="/search/astro-ph?searchtype=author&query=Harra%2C+L+K">L. K. Harra</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1412.5623v1-abstract-short" style="display: inline;"> We investigate the atmospheric response to a small emerging flux region (EFR) that occurred in the positive polarity of Active Region 11236 on 23 \,-\ 24 June 2011. Data from the \textit{Solar Dynamics Observatory's Atmopheric Imaging Assembly} (AIA), the \textit{Helioseismic and Magnetic Imager} (HMI) and Hinode's \textit{EUV imaging spectrometer} (EIS) are used to determine the atmospheric respo… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1412.5623v1-abstract-full').style.display = 'inline'; document.getElementById('1412.5623v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1412.5623v1-abstract-full" style="display: none;"> We investigate the atmospheric response to a small emerging flux region (EFR) that occurred in the positive polarity of Active Region 11236 on 23 \,-\ 24 June 2011. Data from the \textit{Solar Dynamics Observatory's Atmopheric Imaging Assembly} (AIA), the \textit{Helioseismic and Magnetic Imager} (HMI) and Hinode's \textit{EUV imaging spectrometer} (EIS) are used to determine the atmospheric response to new flux emerging into a pre-existing active region. Brightenings are seen forming in the upper photosphere, chromosphere, and corona over the EFR's location whilst flux cancellation is observed in the photosphere. The impact of the flux emergence is far reaching, with new large-scale coronal loops forming up to 43 Mm from the EFR and coronal upflow enhancements of approximately 10 km s$^{-1}$ on the north side of the EFR. Jets are seen forming in the chromosphere and the corona over the emerging serpentine field. This is the first time that coronal jets have been seen over the serpentine field. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1412.5623v1-abstract-full').style.display = 'none'; document.getElementById('1412.5623v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 17 December, 2014; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2014. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">20 pages, 15 figures. Accepted by the Solar Physics journal</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1406.3153">arXiv:1406.3153</a> <span> [<a href="https://arxiv.org/pdf/1406.3153">pdf</a>, <a href="https://arxiv.org/format/1406.3153">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/0004-637X/788/1/85">10.1088/0004-637X/788/1/85 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Coronal magnetic reconnection driven by CME expansion -- the 2011 June 7 event </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">L. van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Baker%2C+D">D. Baker</a>, <a href="/search/astro-ph?searchtype=author&query=Torok%2C+T">T. Torok</a>, <a href="/search/astro-ph?searchtype=author&query=Pariat%2C+E">E. Pariat</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Williams%2C+D+R">D. R. Williams</a>, <a href="/search/astro-ph?searchtype=author&query=Carlyle%2C+J">J. Carlyle</a>, <a href="/search/astro-ph?searchtype=author&query=Valori%2C+G">G. Valori</a>, <a href="/search/astro-ph?searchtype=author&query=Demoulin%2C+P">P. Demoulin</a>, <a href="/search/astro-ph?searchtype=author&query=Kliem%2C+B">B. Kliem</a>, <a href="/search/astro-ph?searchtype=author&query=Long%2C+D+M">D. M. Long</a>, <a href="/search/astro-ph?searchtype=author&query=Matthews%2C+S+A">S. A. Matthews</a>, <a href="/search/astro-ph?searchtype=author&query=Malherbe%2C+J+-">J. -M. Malherbe</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1406.3153v1-abstract-short" style="display: inline;"> Coronal mass ejections (CMEs) erupt and expand in a magnetically structured solar corona. Various indirect observational pieces of evidence have shown that the magnetic field of CMEs reconnects with surrounding magnetic fields, forming, e.g., dimming regions distant from the CME source regions. Analyzing Solar Dynamics Observatory (SDO) observations of the eruption from AR 11226 on 2011 June 7, we… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1406.3153v1-abstract-full').style.display = 'inline'; document.getElementById('1406.3153v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1406.3153v1-abstract-full" style="display: none;"> Coronal mass ejections (CMEs) erupt and expand in a magnetically structured solar corona. Various indirect observational pieces of evidence have shown that the magnetic field of CMEs reconnects with surrounding magnetic fields, forming, e.g., dimming regions distant from the CME source regions. Analyzing Solar Dynamics Observatory (SDO) observations of the eruption from AR 11226 on 2011 June 7, we present the first direct evidence of coronal magnetic reconnection between the fields of two adjacent ARs during a CME. The observations are presented jointly with a data-constrained numerical simulation, demonstrating the formation/intensification of current sheets along a hyperbolic flux tube (HFT) at the interface between the CME and the neighbouring AR 11227. Reconnection resulted in the formation of new magnetic connections between the erupting magnetic structure from AR 11226 and the neighboring active region AR 11227 about 200 Mm from the eruption site. The onset of reconnection first becomes apparent in the SDO/AIA images when filament plasma, originally contained within the erupting flux rope, is re-directed towards remote areas in AR 11227, tracing the change of large-scale magnetic connectivity. The location of the coronal reconnection region becomes bright and directly observable at SDO/AIA wavelengths, owing to the presence of down-flowing cool, dense (10^{10} cm^{-3}) filament plasma in its vicinity. The high-density plasma around the reconnection region is heated to coronal temperatures, presumably by slow-mode shocks and Coulomb collisions. These results provide the first direct observational evidence that CMEs reconnect with surrounding magnetic structures, leading to a large-scale re-configuration of the coronal magnetic field. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1406.3153v1-abstract-full').style.display = 'none'; document.getElementById('1406.3153v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 12 June, 2014; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 2014. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">12 pages, 12 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> The Astrophysical Journal, Volume 788, Issue 1, 85, 12 pp. (2014) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1312.4388">arXiv:1312.4388</a> <span> [<a href="https://arxiv.org/pdf/1312.4388">pdf</a>, <a href="https://arxiv.org/ps/1312.4388">ps</a>, <a href="https://arxiv.org/format/1312.4388">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1017/S1743921313010983">10.1017/S1743921313010983 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Observations of flux rope formation prior to coronal mass ejections </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Kliem%2C+B">Bernhard Kliem</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1312.4388v1-abstract-short" style="display: inline;"> Understanding the magnetic configuration of the source regions of coronal mass ejections (CMEs) is vital in order to determine the trigger and driver of these events. Observations of four CME productive active regions are presented here, which indicate that the pre-eruption magnetic configuration is that of a magnetic flux rope. The flux ropes are formed in the solar atmosphere by the process know… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1312.4388v1-abstract-full').style.display = 'inline'; document.getElementById('1312.4388v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1312.4388v1-abstract-full" style="display: none;"> Understanding the magnetic configuration of the source regions of coronal mass ejections (CMEs) is vital in order to determine the trigger and driver of these events. Observations of four CME productive active regions are presented here, which indicate that the pre-eruption magnetic configuration is that of a magnetic flux rope. The flux ropes are formed in the solar atmosphere by the process known as flux cancellation and are stable for several hours before the eruption. The observations also indicate that the magnetic structure that erupts is not the entire flux rope as initially formed, raising the question of whether the flux rope is able to undergo a partial eruption or whether it undergoes a transition in specific flux rope configuration shortly before the CME. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1312.4388v1-abstract-full').style.display = 'none'; document.getElementById('1312.4388v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 16 December, 2013; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2013. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Proc. IAU Symp. 300 "Nature of prominences and their role in space weather", in press</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1310.0999">arXiv:1310.0999</a> <span> [<a href="https://arxiv.org/pdf/1310.0999">pdf</a>, <a href="https://arxiv.org/ps/1310.0999">ps</a>, <a href="https://arxiv.org/format/1310.0999">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/0004-637X/778/1/69">10.1088/0004-637X/778/1/69 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Plasma composition in a sigmoidal anemone active region </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Baker%2C+D">D. Baker</a>, <a href="/search/astro-ph?searchtype=author&query=Brooks%2C+D+H">D. H. Brooks</a>, <a href="/search/astro-ph?searchtype=author&query=Demoulin%2C+P">P. Demoulin</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">L. van Driel-Gesztelyi</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Steed%2C+K">K. Steed</a>, <a href="/search/astro-ph?searchtype=author&query=Carlyle%2C+J">J. Carlyle</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1310.0999v1-abstract-short" style="display: inline;"> Using spectra obtained by the EIS instrument onboard Hinode, we present a detailed spatially resolved abundance map of an active region (AR)-coronal hole (CH) complex that covers an area of 359 arcsec x 485 arcsec. The abundance map provides first ionization potential (FIP) bias levels in various coronal structures within the large EIS field of view. Overall, FIP bias in the small, relatively youn… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1310.0999v1-abstract-full').style.display = 'inline'; document.getElementById('1310.0999v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1310.0999v1-abstract-full" style="display: none;"> Using spectra obtained by the EIS instrument onboard Hinode, we present a detailed spatially resolved abundance map of an active region (AR)-coronal hole (CH) complex that covers an area of 359 arcsec x 485 arcsec. The abundance map provides first ionization potential (FIP) bias levels in various coronal structures within the large EIS field of view. Overall, FIP bias in the small, relatively young AR is 2-3. This modest FIP bias is a consequence of the AR age, its weak heating, and its partial reconnection with the surrounding CH. Plasma with a coronal composition is concentrated at AR loop footpoints, close to where fractionation is believed to take place in the chromosphere. In the AR, we found a moderate positive correlation of FIP bias with nonthermal velocity and magnetic flux density, both of which are also strongest at the AR loop footpoints. Pathways of slightly enhanced FIP bias are traced along some of the loops connecting opposite polarities within the AR. We interpret the traces of enhanced FIP bias along these loops to be the beginning of fractionated plasma mixing in the loops. Low FIP bias in a sigmoidal channel above the AR's main polarity inversion line where ongoing flux cancellation is taking place, provides new evidence of a bald patch magnetic topology of a sigmoid/flux rope configfiuration. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1310.0999v1-abstract-full').style.display = 'none'; document.getElementById('1310.0999v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 3 October, 2013; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> October 2013. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">For on-line animation, see http://www.mssl.ucl.ac.uk/~db2/fip_intensity.gif. Accepted by ApJ</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1307.2838">arXiv:1307.2838</a> <span> [<a href="https://arxiv.org/pdf/1307.2838">pdf</a>, <a href="https://arxiv.org/format/1307.2838">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1051/0004-6361/201321999">10.1051/0004-6361/201321999 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> First observational application of a connectivity--based helicity flux density </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Dalmasse%2C+K">K. Dalmasse</a>, <a href="/search/astro-ph?searchtype=author&query=Pariat%2C+E">E. Pariat</a>, <a href="/search/astro-ph?searchtype=author&query=Valori%2C+G">G. Valori</a>, <a href="/search/astro-ph?searchtype=author&query=D%C3%A9moulin%2C+P">P. D茅moulin</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1307.2838v1-abstract-short" style="display: inline;"> Measuring the magnetic helicity distribution in the solar corona can help in understanding the trigger of solar eruptive events because magnetic helicity is believed to play a key role in solar activity due to its conservation property. A new method for computing the photospheric distribution of the helicity flux was recently developed. This method takes into account the magnetic field connectivit… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1307.2838v1-abstract-full').style.display = 'inline'; document.getElementById('1307.2838v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1307.2838v1-abstract-full" style="display: none;"> Measuring the magnetic helicity distribution in the solar corona can help in understanding the trigger of solar eruptive events because magnetic helicity is believed to play a key role in solar activity due to its conservation property. A new method for computing the photospheric distribution of the helicity flux was recently developed. This method takes into account the magnetic field connectivity whereas previous methods were based on photospheric signatures only. This novel method maps the true injection of magnetic helicity in active regions. We applied this method for the first time to an observed active region, NOAA 11158, which was the source of intense flaring activity. We used high-resolution vector magnetograms from the SDO/HMI instrument to compute the photospheric flux transport velocities and to perform a nonlinear force-free magnetic field extrapolation. We determined and compared the magnetic helicity flux distribution using a purely photospheric as well as a connectivity-based method. While the new connectivity-based method confirms the mixed pattern of the helicity flux in NOAA 11158, it also reveals a different, and more correct, distribution of the helicity injection. This distribution can be important for explaining the likelihood of an eruption from the active region. The connectivity-based approach is a robust method for computing the magnetic helicity flux, which can be used to study the link between magnetic helicity and eruptivity of observed active regions. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1307.2838v1-abstract-full').style.display = 'none'; document.getElementById('1307.2838v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 10 July, 2013; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> July 2013. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">4 pages, 3 figures; published online in A&A 555, L6 (2013)</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1304.5805">arXiv:1304.5805</a> <span> [<a href="https://arxiv.org/pdf/1304.5805">pdf</a>, <a href="https://arxiv.org/ps/1304.5805">ps</a>, <a href="https://arxiv.org/format/1304.5805">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/1742-6596/440/1/012046">10.1088/1742-6596/440/1/012046 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> On the Seismicity of September 7, 2011 X1.8-class Flare </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Zharkov%2C+S">S. Zharkov</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Matthews%2C+S+A">S. A. Matthews</a>, <a href="/search/astro-ph?searchtype=author&query=Zharkova%2C+V+V">V. V. Zharkova</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1304.5805v1-abstract-short" style="display: inline;"> We present results of our preliminary analysis of acoustically active X-class flare of September 7, 2011. We report two acoustic sources detected via acoustic holography and verified by finding a ridge in time-distance diagrams. We compare the directional information extracted from time-distance and acoustic holography, showing a good agreement in this case. We report that the direction where ampl… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1304.5805v1-abstract-full').style.display = 'inline'; document.getElementById('1304.5805v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1304.5805v1-abstract-full" style="display: none;"> We present results of our preliminary analysis of acoustically active X-class flare of September 7, 2011. We report two acoustic sources detected via acoustic holography and verified by finding a ridge in time-distance diagrams. We compare the directional information extracted from time-distance and acoustic holography, showing a good agreement in this case. We report that the direction where amplitude of the wave-front is the largest lies through the strong magnetic field and sunspot, suggesting that absorption of the acoustic wave power by magnetic field can be ruled out as a wave anisotropy mechanism in this case. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1304.5805v1-abstract-full').style.display = 'none'; document.getElementById('1304.5805v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 21 April, 2013; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2013. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Proceedings of "Eclipse on the Coral Sea: Cycle 24 Ascending GONG 2012/LWS/SDO-5/SOHO-27" meeting, November 12-16, 2012, Palm Cove, Queensland</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1208.4284">arXiv:1208.4284</a> <span> [<a href="https://arxiv.org/pdf/1208.4284">pdf</a>, <a href="https://arxiv.org/ps/1208.4284">ps</a>, <a href="https://arxiv.org/format/1208.4284">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1007/s11207-012-0169-4">10.1007/s11207-012-0169-4 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Properties of the 15 February 2011 Flare Seismic Sources </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Zharkov%2C+S">S. Zharkov</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Matthews%2C+S+A">S. A. Matthews</a>, <a href="/search/astro-ph?searchtype=author&query=Zharkova%2C+V+V">V. V. Zharkova</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1208.4284v1-abstract-short" style="display: inline;"> The first near-side X-class flare of the Solar Cycle 24 occurred in February 2011 and produced a very strong seismic response in the photosphere. One sunquake was reported by Kosovichev (2011) followed by the discovery of a second sunquake by Zharkov et al (2011). The flare had a two-ribbon structure and was associated with a flux rope eruption and a halo coronal mass ejection (CME) as reported in… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1208.4284v1-abstract-full').style.display = 'inline'; document.getElementById('1208.4284v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1208.4284v1-abstract-full" style="display: none;"> The first near-side X-class flare of the Solar Cycle 24 occurred in February 2011 and produced a very strong seismic response in the photosphere. One sunquake was reported by Kosovichev (2011) followed by the discovery of a second sunquake by Zharkov et al (2011). The flare had a two-ribbon structure and was associated with a flux rope eruption and a halo coronal mass ejection (CME) as reported in the CACTus catalogue. Following the discovery of the second sunquake and the spatial association of both sources with the locations of the feet of the erupting flux rope (Zharkov et al 2011) we present here a more detailed analysis of the observed photospheric changes in and around the seismic sources. These sunquakes are quite unusual, taking place early in the impulsive stage of the flare, with the seismic sources showing little hard X-ray (HXR) emission, and strongest X-ray emission sources located in the flare ribbons. We present a directional time--distance diagram computed for the second source, which clearly shows a ridge corresponding to the travelling acoustic wave packet and find that the quake at the second source happened about 45 seconds to one minute earlier than the first source. Using acoustic holography we report different frequency responses of the two sources. We find strong downflows at both seismic locations and a supersonic horizontal motion at the second site of acoustic wave excitation. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1208.4284v1-abstract-full').style.display = 'none'; document.getElementById('1208.4284v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 21 August, 2012; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2012. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">15 pages, 5 figures, accepted for publication by Solar Physics</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1110.2005">arXiv:1110.2005</a> <span> [<a href="https://arxiv.org/pdf/1110.2005">pdf</a>, <a href="https://arxiv.org/ps/1110.2005">ps</a>, <a href="https://arxiv.org/format/1110.2005">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/2041-8205/741/2/L35">10.1088/2041-8205/741/2/L35 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> February 15, 2011: sun-quakes produced by flux rope eruption </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Zharkov%2C+S">S. Zharkov</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Matthews%2C+S+A">S. A. Matthews</a>, <a href="/search/astro-ph?searchtype=author&query=Zharkova%2C+V+V">V. V. Zharkova</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1110.2005v1-abstract-short" style="display: inline;"> We present an analysis of the 15 February 2011 X-class solar flare, previously reported to produce the first sunquake in solar cycle 24 (Kosovichev 2011). Using acoustic holography, we confirm the first, and report a second, weaker, seismic source associated with this flare. We find that the two sources are located at either end of a sigmoid which indicates the presence of a flux rope. Contrary to… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1110.2005v1-abstract-full').style.display = 'inline'; document.getElementById('1110.2005v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1110.2005v1-abstract-full" style="display: none;"> We present an analysis of the 15 February 2011 X-class solar flare, previously reported to produce the first sunquake in solar cycle 24 (Kosovichev 2011). Using acoustic holography, we confirm the first, and report a second, weaker, seismic source associated with this flare. We find that the two sources are located at either end of a sigmoid which indicates the presence of a flux rope. Contrary to the majority of previously reported sunquakes, the acoustic emission precedes the peak of major hard X-ray (HXR) sources by several minutes. Furthermore, the strongest hard X-ray footpoints derived from RHESSI data are found to be located away from the seismic sources in the flare ribbons. We account for these discrepancies within the context of a phenomenological model of a flux rope eruption and accompanying two-ribbon flare. We propose that the sunquakes are triggered at the footpoints of the erupting flux rope at the start of the flare impulsive phase and eruption onset, while the main hard X-ray sources appear later at the footpoints of the flare loops formed under the rising flux rope. Possible implications of this scenario for the theoretical interpretation of the forces driving sunquakes are discussed. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1110.2005v1-abstract-full').style.display = 'none'; document.getElementById('1110.2005v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 10 October, 2011; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> October 2011. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">15 pages, 5 figures, 1 online movie, accepted for publication in ApJL</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1102.5296">arXiv:1102.5296</a> <span> [<a href="https://arxiv.org/pdf/1102.5296">pdf</a>, <a href="https://arxiv.org/format/1102.5296">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Instrumentation and Methods for Astrophysics">astro-ph.IM</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Space Physics">physics.space-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/0004-637X/729/2/97">10.1088/0004-637X/729/2/97 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Modeling the Dispersal of an Active Region: Quantifying Energy Input into the Corona </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Mackay%2C+D+H">Duncan H. Mackay</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=van+Ballegooijen%2C+A">Aad van Ballegooijen</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1102.5296v1-abstract-short" style="display: inline;"> In this paper a new technique for modeling non-linear force-free fields directly from line of sight magnetogram observations is presented. The technique uses sequences of magnetograms directly as lower boundary conditions to drive the evolution of coronal magnetic fields between successive force-free equilibria over long periods of time. It is illustrated by applying it to MDI observations of a de… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1102.5296v1-abstract-full').style.display = 'inline'; document.getElementById('1102.5296v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1102.5296v1-abstract-full" style="display: none;"> In this paper a new technique for modeling non-linear force-free fields directly from line of sight magnetogram observations is presented. The technique uses sequences of magnetograms directly as lower boundary conditions to drive the evolution of coronal magnetic fields between successive force-free equilibria over long periods of time. It is illustrated by applying it to MDI observations of a decaying active region, NOAA AR 8005. The active region is modeled during a 4 day period around its central meridian passage. Over this time, the dispersal of the active region is dominated by random motions due to small scale convective cells. Through studying the build up of magnetic energy in the model, it is found that such small scale motions may inject anywhere from $2.5-3 \times 10^{25}$ erg s$^{-1}$ of free magnetic energy into the coronal field. Most of this energy is stored within the center of the active region in the low corona, below 30 Mm. After 4 days the build-up of free energy is 10% that of the corresponding potential field. This energy buildup, is sufficient to explain the radiative losses at coronal temperatures within the active region. Small scale convective motions therefore play an integral part in the energy balance of the corona. This new technique has wide ranging applications with the new high resolution, high cadence observations from the SDO:HMI and SDO:AIA instruments. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1102.5296v1-abstract-full').style.display = 'none'; document.getElementById('1102.5296v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 25 February, 2011; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 2011. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">13 Figures, 2 movies</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> ApJ, 729, 97 (2011) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1011.1227">arXiv:1011.1227</a> <span> [<a href="https://arxiv.org/pdf/1011.1227">pdf</a>, <a href="https://arxiv.org/ps/1011.1227">ps</a>, <a href="https://arxiv.org/format/1011.1227">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1051/0004-6361/201015146">10.1051/0004-6361/201015146 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Photospheric flux cancellation and associated flux rope formation and eruption </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Kliem%2C+B">B. Kliem</a>, <a href="/search/astro-ph?searchtype=author&query=Wallace%2C+A+J">A. J. Wallace</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1011.1227v1-abstract-short" style="display: inline;"> We study an evolving bipolar active region that exhibits flux cancellation at the internal polarity inversion line, the formation of a soft X-ray sigmoid along the inversion line and a coronal mass ejection. The evolution of the photospheric magnetic field is described and used to estimate how much flux is reconnected into the flux rope. About one third of the active region flux cancels at the int… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1011.1227v1-abstract-full').style.display = 'inline'; document.getElementById('1011.1227v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1011.1227v1-abstract-full" style="display: none;"> We study an evolving bipolar active region that exhibits flux cancellation at the internal polarity inversion line, the formation of a soft X-ray sigmoid along the inversion line and a coronal mass ejection. The evolution of the photospheric magnetic field is described and used to estimate how much flux is reconnected into the flux rope. About one third of the active region flux cancels at the internal polarity inversion line in the 2.5~days leading up to the eruption. In this period, the coronal structure evolves from a weakly to a highly sheared arcade and then to a sigmoid that crosses the inversion line in the inverse direction. These properties suggest that a flux rope has formed prior to the eruption. The amount of cancellation implies that up to 60% of the active region flux could be in the body of the flux rope. We point out that only part of the cancellation contributes to the flux in the rope if the arcade is only weakly sheared, as in the first part of the evolution. This reduces the estimated flux in the rope to $\sim\!30%$ or less of the active region flux. We suggest that the remaining discrepancy between our estimate and the limiting value of $\sim\!10%$ of the active region flux, obtained previously by the flux rope insertion method, results from the incomplete coherence of the flux rope, due to nonuniform cancellation along the polarity inversion line. A hot linear feature is observed in the active region which rises as part of the eruption and then likely traces out field lines close to the axis of the flux rope. The flux cancellation and changing magnetic connections at one end of this feature suggest that the flux rope reaches coherence by reconnection shortly before and early in the impulsive phase of the associated flare. The sigmoid is destroyed in the eruption but reforms within a few hours after a moderate amount of further cancellation has occurred. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1011.1227v1-abstract-full').style.display = 'none'; document.getElementById('1011.1227v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 4 November, 2010; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2010. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Astron. Astrophys., in press</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/0906.4794">arXiv:0906.4794</a> <span> [<a href="https://arxiv.org/pdf/0906.4794">pdf</a>, <a href="https://arxiv.org/ps/0906.4794">ps</a>, <a href="https://arxiv.org/format/0906.4794">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/0004-637X/700/2/L83">10.1088/0004-637X/700/2/L83 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Flux Rope Formation Preceding Coronal Mass Ejection Onset </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Kliem%2C+B">B. Kliem</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="0906.4794v1-abstract-short" style="display: inline;"> We analyse the evolution of a sigmoidal (S shaped) active region toward eruption, which includes a coronal mass ejection (CME) but leaves part of the filament in place. The X-ray sigmoid is found to trace out three different magnetic topologies in succession: a highly sheared arcade of coronal loops in its long-lived phase, a bald-patch separatrix surface (BPSS) in the hours before the CME, and… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0906.4794v1-abstract-full').style.display = 'inline'; document.getElementById('0906.4794v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="0906.4794v1-abstract-full" style="display: none;"> We analyse the evolution of a sigmoidal (S shaped) active region toward eruption, which includes a coronal mass ejection (CME) but leaves part of the filament in place. The X-ray sigmoid is found to trace out three different magnetic topologies in succession: a highly sheared arcade of coronal loops in its long-lived phase, a bald-patch separatrix surface (BPSS) in the hours before the CME, and the first flare loops in its major transient intensity enhancement. The coronal evolution is driven by photospheric changes which involve the convergence and cancellation of flux elements under the sigmoid and filament. The data yield unambiguous evidence for the existence of a BPSS, and hence a flux rope, in the corona prior to the onset of the CME. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0906.4794v1-abstract-full').style.display = 'none'; document.getElementById('0906.4794v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 26 June, 2009; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 2009. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">ApJ Letters, in press</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Astrophys.J.700:L83-L87,2009 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/0904.4782">arXiv:0904.4782</a> <span> [<a href="https://arxiv.org/pdf/0904.4782">pdf</a>, <a href="https://arxiv.org/ps/0904.4782">ps</a>, <a href="https://arxiv.org/format/0904.4782">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/0004-637X/698/1/L27">10.1088/0004-637X/698/1/L27 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Temperature Tomography of a Coronal Sigmoid Supporting the Gradual Formation of a Flux Rope </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Tripathi%2C+D">Durgesh Tripathi</a>, <a href="/search/astro-ph?searchtype=author&query=Kliem%2C+B">Bernhard Kliem</a>, <a href="/search/astro-ph?searchtype=author&query=Mason%2C+H+E">Helen E. Mason</a>, <a href="/search/astro-ph?searchtype=author&query=Young%2C+P">Peter Young</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">Lucie M. Green</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="0904.4782v1-abstract-short" style="display: inline;"> Multi-wavelength observations of a sigmoidal (S-shaped) solar coronal source by the EUV Imaging Spectrometer and the X-ray Telescope aboard the Hinode spacecraft and by the EUV Imager aboard STEREO are reported. The data reveal the coexistence of a pair of J-shaped hot arcs at temperatures T>2 MK with an S-shaped structure at somewhat lower temperatures T~1.3 MK. The middle section of the S-shap… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0904.4782v1-abstract-full').style.display = 'inline'; document.getElementById('0904.4782v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="0904.4782v1-abstract-full" style="display: none;"> Multi-wavelength observations of a sigmoidal (S-shaped) solar coronal source by the EUV Imaging Spectrometer and the X-ray Telescope aboard the Hinode spacecraft and by the EUV Imager aboard STEREO are reported. The data reveal the coexistence of a pair of J-shaped hot arcs at temperatures T>2 MK with an S-shaped structure at somewhat lower temperatures T~1.3 MK. The middle section of the S-shaped structure runs along the polarity inversion line of the photospheric field, bridging the gap between the arcs. Flux cancellation occurs at the same location in the photosphere. The sigmoid forms in the gradual decay phase of the active region, which does not experience an eruption. These findings correspond to the expected signatures of a flux rope forming, or being augmented, gradually by a topology transformation inside a magnetic arcade. In such a transformation, the plasma on newly formed helical field lines in the outer flux shell of the rope (S-shaped in projection) is expected to enter a cooling phase once the reconnection of their parent field line pairs (double-J shaped in projection) is complete. Thus, the data support the conjecture that flux ropes can exist in the corona prior to eruptive activity. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0904.4782v1-abstract-full').style.display = 'none'; document.getElementById('0904.4782v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 30 April, 2009; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2009. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">15 pages, 5 figures, Accepted for publication in ApJ Letters</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Astrophys.J.698:L27-L32,2009 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0304092">arXiv:astro-ph/0304092</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0304092">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0304092">ps</a>, <a href="https://arxiv.org/format/astro-ph/0304092">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1023/A:1025678917086">10.1023/A:1025678917086 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> How are Emerging Flux, Flares and CMEs Related to Magnetic Polarity Imbalance in MDI Data? </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Green%2C+L+M">L. M. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Demoulin%2C+P">P. Demoulin</a>, <a href="/search/astro-ph?searchtype=author&query=Mandrini%2C+C+H">C. H. Mandrini</a>, <a href="/search/astro-ph?searchtype=author&query=van+Driel-Gesztelyi%2C+L">L. van Driel-Gesztelyi</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0304092v1-abstract-short" style="display: inline;"> In order to understand whether major flares or coronal mass ejections (CMEs) can be related to changes in the longitudinal photospheric magnetic field, we study 4 young active regions during seven days of their disc passage. This time period precludes any biases which may be introduced in studies that look at the field evolution during the short-term flare or CME period only. Data from the Miche… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0304092v1-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0304092v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0304092v1-abstract-full" style="display: none;"> In order to understand whether major flares or coronal mass ejections (CMEs) can be related to changes in the longitudinal photospheric magnetic field, we study 4 young active regions during seven days of their disc passage. This time period precludes any biases which may be introduced in studies that look at the field evolution during the short-term flare or CME period only. Data from the Michelson Doppler Imager (MDI) with a time cadence of 96 minutes are used. Corrections are made to the data to account for area foreshortening and angle between line of sight and field direction, and also the underestimation of the flux densities. We make a systematic study of the evolution of the longitudinal magnetic field, and analyze flare and CME occurrence in the magnetic evolution. We find that the majority of CMEs and flares occur during or after new flux emergence. The flux in all four active regions is observed to have deviations from polarity balance both on the long-term (solar rotation) and on the short term (few hours). The long-term imbalance is not due to linkage outside the active region; it is primarily related to the east-west distance from central meridian, with the sign of polarity closer to the limb dominating. The sequence of short term imbalances are not closely linked to CMEs and flares and no permanent imbalance remains after them. We propose that both kinds of imbalance are due to the presence of a horizontal field component (parallel to the photospheric surface) in the emerging flux. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0304092v1-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0304092v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 4 April, 2003; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2003. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">22 pages, 8 figures, Solar Physics (in press)</span> </p> </li> </ol> <div class="is-hidden-tablet">  <span class="help" style="display: inline-block;"><a href="https://github.com/arXiv/arxiv-search/releases">Search v0.5.6 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