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Funding: UK STFC via PhD studentship and the Consolidated Grant SMC1/YST025 (S.L.Y.); STFC and Leverhulme trust (D.H.M.). 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 Hα 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 4x1020 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 3.2x1020 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 x 1031 ergs. Postprint

We propose that the plasma physics community and funding agencies invest in an open source software ecosystem for plasma research and education., This community paper was submitted to the Plasma 2020 decadal review of plasma physics., {"references":["D. Muna et al. (2016), \"The Astropy Problem,\" arXiv:1610.03159","Astropy Collaboration et al. (2018), \"The Astropy Project: Building an Open-science Project and Status of the v2.0 Core Package,\" Astronomical Journal 156, 123, doi:10.3847/1538-3881/aabc4f","SunPy Community et al. (2015), \"SunPy – Python for solar physics,\" Computational Science and Discovery 8, 1, doi:10.1088/1749-4699/8/1/014009","A. Burrell et al. (2018), \"Snakes on a Spaceship – An Overview of Python in Heliophysics,\" Journal of Geophysical Research 123, 10384, doi:10.1029/2018JA025877","PlasmaPy Community et al. (2018), \"PlasmaPy: an open source community-developed Python package for plasma physics,\" Zenodo, doi:10.5281/zenodo.1238132","National Academies of Sciences, Engineering, and Medicine, \"Open Source Software Policy Options for NASA Earth and Space Sciences\" (National Academies Press, 2018).","S. Hettrick (2016), \"Research Software Sustainability: Report on a Knowledge Exchange Workshop.\"","Mark D. Wilkinson et al. (2016), \"The FAIR Guiding Principles for scientific data management and stewardship,\" Scientific Data 3, sdata201618, doi:10.1038/sdata.2016.18","Engineering and Physical Sciences Research Council, \"Software as an infrastructure,\" (2012).","G. Wilson et al. (2014), \"Best Practices for Scientific Computing,\" PLOS Biology 12, 1, doi:10.1371/journal.pbio.1001745","A. Scopatz and K. D. Huff, \"Effective Computation in Physics: Field Guide to Research with Python\" (O'Reilly Media, 2015).","B. K. Spears et al. (2018), \"Deep learning: A guide for practitioners in the physical sciences,\" Physics of Plasmas 25, 080901, doi:10.1063/1.5020791","D. R. Smith et al., \"Highlights from the community white paper 'Enhancing US fusion science with data- centric technologies',\" in APS DPP Meeting Abstracts (2018)."]}

We study the properties of the local transverse deviations of magnetic field lines at a fixed moment in time. Those deviations "evolve" smoothly in a plane normal to the field-line direction as one moves that plane along the field line. Since the evolution can be described by a planar flow in the normal plane, we derive most of our results in the context of a toy model for planar fluid flow. We then generalize our results to include the effects of field-line curvature. We show that the type of flow is determined by the two non-zero eigenvalues of the gradient of the normalized magnetic field. The eigenvalue difference quantifies the local rate of squeezing or coiling of neighboring field lines, which we relate to standard notions of fluid vorticity and shear. The resulting squeezing rate can be used in the detection of null points, hyperbolic flux tubes and current sheets. Once integrated along field lines, that rate gives a squeeze factor, which is an approximation to the squashing factor, which is usually employed in locating quasi-separatrix layers (QSLs), which are possible sites for magnetic reconnection. Unlike the squeeze factor, the squashing factor can miss QSLs for which field lines are squeezed and then unsqueezed. In that regard, the squeeze factor is a better proxy for locating QSLs than the squashing factor. In another application of our analysis, we construct an approximation to the local rate of twist of neighboring field lines, which we refer to as the coiling rate. That rate can be integrated along a field line to give a coiling number, $\mathrm{N_c}$. We show that unlike the standard local twist number, $\mathrm{N_c}$ gives an unbiased approximation to the number of twists neighboring field lines make around one another. $\mathrm{N_c}$ can be useful for the study of flux rope instabilities, such as the kink instability, and can be used in the detection of flux ropes., 48 pages, 6 figures

Accepted: 2007-08-26, 資料番号: SA1000265000

International audience

International audience

Throughout the eleven year cycle of the sun, solar eruptions are constantly taking place. Thought to be caused by reconnection of magnetic field lines, coronal jets are one of several types of such eruptions. Jet formation and eruption is not well understood. In some cases, jets occur when small filaments of chromospheric material are lofted into the corona. The filaments have strong magnetic flux, and are often the site of magnetic reconnection and subsequent eruption. In order to better understand the constraints on these coronal jets, we have modeled the conditions required for stable filaments and eruptions using nonlinear force-free (NLFF) field modeling. NLFF models are 3-D topological models that are used to show the morphological evolution of magnetic fields. Using the CMS2 modeling suite, we modeled two regions with jet eruptions: a coronal jet near a larger filament, and a coronal jet near an AR sigmoid. In both cases, Solar Dynamics Observatory’s HMI magnetograms and observations from AIA images are used to constrain the input parameters of the model. In this presentation, we will present our model results and discuss how they help understand solar coronal jet eruptions., This work is supported by NSF-REU solar physics program at SAO, grant number AGS-1560313, and NASA grant number NNX15AF43G.

In this study, the magnetic configuration of a coronal sigmoid is presented. The sigmoid was observed by Hinode/XRT and SDO/AIA in the NOAA active region 12665 between July 6th-18th, 2017. We construct a Non-Linear Force-Free Field (NLFFF) model of a sigmoid observed on July 13th 2017 at 18:22 UTC using the flux-rope insertion (FR) method and relaxed the magnetic field toward a force-free state using magnetofrictional relaxation (MF). The NLFFF model produces the 3D coronal magnetic field constrained by observed coronal structures and photospheric magnetograms. SDO/HMI magnetograms were used as input of the models. The resulting magnetic field configurations were compared with Hinode/XRT and SDO/AIA images of the same region to determine the best-fit model. The sigmoid is modeled in both stable and unstable states to represent various stages of evolution in the sigmoid; the best-fit stable model has a poloidal flux of -3E10 Mx and axial flux of 2E21 Mx, whereas the best-fit unstable model has a poloidal flux of -1E10 and an axial flux of 5e21. Additionally, similar models were produced for a time earlier in the development of the active region on July 12th, 2017 at 03:17 UTC where a small jet is observed in the elbow of the sigmoid. The goal of our study is to reproduce the pre-flare configuration so that we can understand the eruption and have a NLFFF model for the magnetic environment in which the jet is erupting., This work was supported by NSF-REU Solar Physics program at SAO, grant number AGS-1560313

Jets are small explosions that occur frequently in the Sun possibly driven by the local reconfiguration of the magnetic field, or reconnection. There are two types of coronal jets: standard jets and blowout jets. The purpose of this project is to determine which mechanisms accelerate plasma in two different jets, one that occurred in January 17, 2015 at the disk of the sun and another in October 24, 2015 at the limb. Two possible acceleration mechanisms are chromospheric evaporation and magnetic acceleration. Using SDO/AIA, Hinode/XRT and IRIS data, we create height-time plots, and calculate the velocities of each wavelength for both jets. We calculate the potential magnetic field of the jet and the general region around it to gain a more detailed understanding of its structure, and determine if the jet is likely to be either a standard or blowout jet. Finally, we calculate the magnetic field strength for different heights along the jet spire, and use differential emission measures to calculate the plasma density. Once we have these two values, we calculate the Alfven speed. When analyzing our results we are looking for certain patterns in our velocities. If the plasma in a jet is accelerated by chromospheric evaporation, we expect the velocities to increase as function of temperature, which is what we observed in the October 24th jet. The magnetic models for this jet also show the Eiffel Tower shaped structure characteristic of standard jets, which tend to have plasma accelerated by this mechanism. On the other hand, if the acceleration mechanism were magnetic acceleration, we would expect the velocities to be similar regardless of temperature. For the January 17th jet, we saw that along the spire, the velocities where approximately 200 km/s in all wavelengths, but the velocities of hot plasma detected at the base were closer to the Alfven speed, which was estimated to be about 2,000 km/s. These observations suggest that the plasma in the January 17th jet is magnetically accelerated. The magnetic model for this jet needs to be studied further by using a NLFFF magnetic field model and not just the potential magnetic field.

The structure of energy storing magnetic field lines on the Sun is very twisted and contorted. Some of the twist arises from photospheric foot point motion and some is due to currents carried into the corona as fields emerge. The stability of a region depends on both the energy stored (so-called “free” energy) and on the structure of the surrounding nearly potential fields. Free energy is usually contained in these S-shaped regions called sigmoids on the solar corona. The only way to reach lower energy state is to release this free energy, by changing its connectivity. This change in connectivity leads to flares and coronal mass ejections (CMEs) that can affect environments of nearby planets. For this project, we focus on a special kind of connectivity change called slip-running reconnection to create 3D numerical models of flare-producing magnetic fields. By comparing these numerical models to observational data from Atmospheric Imaging Assembly (AIA), we will be able to better explain the evolution of sigmoidal flares from active regions. We are studying a flare from Dudik et al 2014 paper (2012 July 12), and a flare from 2015 June 14. Using the Coronal Modeling System (CMS) software, we read the photospheric magnetogram for the specified date and time, compute the potential field, setup the 3D flux rope path, and then relax this flux rope over 60,000 iterations to create a nonlinear force-free field (NLFFF). Using these relaxed models we find the best-fit loops surrounding the flux rope. We then compare these models to the observations in AIA. We compare the magnetic field structure in our models with the observed slipping. For regions near our inserted flux rope, our models successfully correlate with this observation. Further modeling is required, but these initial results suggest that NLFFF modeling may be able to capture realistic 3-D magnetic structures associated with slipping reconnection.

Final presentations of the Center for Astrophysics HEA/SSP Solar Summer Intern Program.

Final presentations of the Center for Astrophysics HEA/SSP Solar Summer Intern Program.

Final presentations of Center for Astrophysics HEA/SSP Solar Summer Intern Program.