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Magnetic reconnection in partially ionized plasmasNi, LeiJi, HantaoMurphy, Nicholas A.Jara-Almonte, JonathanDOI: info:10.1098/rspa.2019.0867v. 47690867
Ni, Lei, Ji, Hantao, Murphy, Nicholas A., and Jara-Almonte, Jonathan. 2020. "Magnetic reconnection in partially ionized plasmas." Proceedings of the Royal Society of London Series A 476:90867. https://doi.org/10.1098/rspa.2019.0867
ID: 158874
Type: article
Authors: Ni, Lei; Ji, Hantao; Murphy, Nicholas A.; Jara-Almonte, Jonathan
Abstract: Magnetic reconnection has been intensively studied in fully ionized plasmas. However, plasmas are often partially ionized in astrophysical environments. The interactions between the neutral particles and ionized plasmas might strongly affect the reconnection mechanisms. We review magnetic reconnection in partially ionized plasmas in different environments from theoretical, numerical, observational and experimental points of view. We focus on mechanisms which make magnetic reconnection fast enough to compare with observations, especially on the reconnection events in the low solar atmosphere. The heating mechanisms and the related observational evidence of the reconnection process in the partially ionized low solar atmosphere are also discussed. We describe magnetic reconnection in weakly ionized astrophysical environments, including the interstellar medium and protostellar disks. We present recent achievements about fast reconnection in laboratory experiments for partially ionized plasmas.
Exploring Plasma Heating in the Current Sheet Region in a Three-dimensional Coronal Mass Ejection SimulationReeves, Katharine K.Török, TiborMikić, ZoranLinker, JonMurphy, Nicholas A.DOI: info:10.3847/1538-4357/ab4ce8v. 887103
Reeves, Katharine K., Török, Tibor, Mikić, Zoran, Linker, Jon, and Murphy, Nicholas A. 2019. "Exploring Plasma Heating in the Current Sheet Region in a Three-dimensional Coronal Mass Ejection Simulation." The Astrophysical Journal 887:103. https://doi.org/10.3847/1538-4357/ab4ce8
ID: 154513
Type: article
Authors: Reeves, Katharine K.; Török, Tibor; Mikić, Zoran; Linker, Jon; Murphy, Nicholas A.
Abstract: We simulate a coronal mass ejection using a three-dimensional magnetohydrodynamic code that includes coronal heating, thermal conduction, and radiative cooling in the energy equation. The magnetic flux distribution at 1 R s is produced by a localized subsurface dipole superimposed on a global dipole field, mimicking the presence of an active region within the global corona. Transverse electric fields are applied near the polarity inversion line to introduce a transverse magnetic field, followed by the imposition of a converging flow to form and destabilize a flux rope, producing an eruption. We examine the quantities responsible for plasma heating and cooling during the eruption, including thermal conduction, radiation, adiabatic effects, coronal heating, and ohmic heating. We find that ohmic heating is an important contributor to hot temperatures in the current sheet region early in the eruption, but in the late phase, adiabatic compression plays an important role in heating the plasma there. Thermal conduction also plays an important role in the transport of thermal energy away from the current sheet region throughout the reconnection process, producing a "thermal halo" and widening the region of high temperatures. We simulate emission from solar telescopes for this eruption and find that there is evidence for emission from heated plasma above the flare loops late in the eruption, when the adiabatic heating is the dominant heating term. These results provide an explanation for hot supra-arcade plasma sheets that are often observed in X-rays and extreme ultraviolet wavelengths during the decay phase of large flares.
The Astropy Project: Building an Open-science Project and Status of the v2.0 Core PackageAstropy CollaborationPrice-Whelan, A. M.Sipőcz, B. M.Günther, H. M.Lim, P. L.Crawford, S. M.Conseil, S.Shupe, D. L.Craig, M. W.Dencheva, N.Ginsburg, A.VanderPlas, J. T.Bradley, L. D.Pérez-Suárez, D.de Val-Borro, M.Aldcroft, T. L.Cruz, K. L.Robitaille, T. P.Tollerud, E. J.Ardelean, C.Babej, T.Bach, Y. P.Bachetti, M.Bakanov, A. V.Bamford, S. P.Barentsen, G.Barmby, P.Baumbach, A.Berry, K. L.Biscani, F.Boquien, M.Bostroem, K. A.Bouma, L. G.Brammer, G. B.Bray, E. M.Breytenbach, H.Buddelmeijer, H.Burke, D. J.Calderone, G.Cano Rodríguez, J. L.Cara, M.Cardoso, J. V. M.Cheedella, S.Copin, Y.Corrales, L.Crichton, D.D'Avella, D.Deil, C.Depagne, É.Dietrich, J. P.Donath, A.Droettboom, M.Earl, N.Erben, T.Fabbro, S.Ferreira, L. A.Finethy, T.Fox, R. T.Garrison, L. H.Gibbons, S. L. J.Goldstein, D. A.Gommers, R.Greco, J. P.Greenfield, P.Groener, A. M.Grollier, F.Hagen, A.Hirst, P.Homeier, D.Horton, A. J.Hosseinzadeh, G.Hu, L.Hunkeler, J. S.Ivezić, Ž.Jain, A.Jenness, T.Kanarek, G.Kendrew, S.Kern, N. S.Kerzendorf, W. E.Khvalko, A.King, J.Kirkby, D.Kulkarni, A. M.Kumar, A.Lee, A.Lenz, D.Littlefair, S. P.Ma, Z.Macleod, D. M.Mastropietro, M.McCully, C.Montagnac, S.Morris, B. M.Mueller, M.Mumford, S. J.Muna, D.Murphy, N. A.Nelson, S.Nguyen, G. H.Ninan, J. P.Nöthe, M.Ogaz, S.Oh, S.Parejko, J. K.Parley, N.Pascual, S.Patil, R.Patil, A. A.Plunkett, A. L.Prochaska, J. X.Rastogi, T.Reddy Janga, V.Sabater, J.Sakurikar, P.Seifert, M.Sherbert, L. E.Sherwood-Taylor, H.Shih, A. Y.Sick, J.Silbiger, M. T.Singanamalla, S.Singer, L. P.Sladen, P. H.Sooley, K. A.Sornarajah, S.Streicher, O.Teuben, P.Thomas, S. W.Tremblay, Grant R.Turner, J. E. H.Terrón, V.van Kerkwijk, M. H.de la Vega, A.Watkins, L. L.Weaver, B. A.Whitmore, J. B.Woillez, J.Zabalza, V.Astropy ContributorsDOI: info:10.3847/1538-3881/aabc4fv. 156123
Astropy Collaboration, Price-Whelan, A. M., Sipőcz, B. M., Günther, H. M., Lim, P. L., Crawford, S. M., Conseil, S., Shupe, D. L., Craig, M. W., Dencheva, N., Ginsburg, A., VanderPlas, J. T., Bradley, L. D., Pérez-Suárez, D., de Val-Borro, M., Aldcroft, T. L., Cruz, K. L., Robitaille, T. P., Tollerud, E. J., Ardelean, C., Babej, T., Bach, Y. P., Bachetti, M., Bakanov, A. V., Bamford, S. P. et al. 2018. "The Astropy Project: Building an Open-science Project and Status of the v2.0 Core Package." The Astronomical Journal 156:123. https://doi.org/10.3847/1538-3881/aabc4f
ID: 149183
Type: article
Authors: Astropy Collaboration; Price-Whelan, A. M.; Sipőcz, B. M.; Günther, H. M.; Lim, P. L.; Crawford, S. M.; Conseil, S.; Shupe, D. L.; Craig, M. W.; Dencheva, N.; Ginsburg, A.; VanderPlas, J. T.; Bradley, L. D.; Pérez-Suárez, D.; de Val-Borro, M.; Aldcroft, T. L.; Cruz, K. L.; Robitaille, T. P.; Tollerud, E. J.; Ardelean, C.; Babej, T.; Bach, Y. P.; Bachetti, M.; Bakanov, A. V.; Bamford, S. P.; Barentsen, G.; Barmby, P.; Baumbach, A.; Berry, K. L.; Biscani, F.; Boquien, M.; Bostroem, K. A.; Bouma, L. G.; Brammer, G. B.; Bray, E. M.; Breytenbach, H.; Buddelmeijer, H.; Burke, D. J.; Calderone, G.; Cano Rodríguez, J. L.; Cara, M.; Cardoso, J. V. M.; Cheedella, S.; Copin, Y.; Corrales, L.; Crichton, D.; D'Avella, D.; Deil, C.; Depagne, É.; Dietrich, J. P.; Donath, A.; Droettboom, M.; Earl, N.; Erben, T.; Fabbro, S.; Ferreira, L. A.; Finethy, T.; Fox, R. T.; Garrison, L. H.; Gibbons, S. L. J.; Goldstein, D. A.; Gommers, R.; Greco, J. P.; Greenfield, P.; Groener, A. M.; Grollier, F.; Hagen, A.; Hirst, P.; Homeier, D.; Horton, A. J.; Hosseinzadeh, G.; Hu, L.; Hunkeler, J. S.; Ivezić, Ž.; Jain, A.; Jenness, T.; Kanarek, G.; Kendrew, S.; Kern, N. S.; Kerzendorf, W. E.; Khvalko, A.; King, J.; Kirkby, D.; Kulkarni, A. M.; Kumar, A.; Lee, A.; Lenz, D.; Littlefair, S. P.; Ma, Z.; Macleod, D. M.; Mastropietro, M.; McCully, C.; Montagnac, S.; Morris, B. M.; Mueller, M.; Mumford, S. J.; Muna, D.; Murphy, N. A.; Nelson, S.; Nguyen, G. H.; Ninan, J. P.; Nöthe, M.; Ogaz, S.; Oh, S.; Parejko, J. K.; Parley, N.; Pascual, S.; Patil, R.; Patil, A. A.; Plunkett, A. L.; Prochaska, J. X.; Rastogi, T.; Reddy Janga, V.; Sabater, J.; Sakurikar, P.; Seifert, M.; Sherbert, L. E.; Sherwood-Taylor, H.; Shih, A. Y.; Sick, J.; Silbiger, M. T.; Singanamalla, S.; Singer, L. P.; Sladen, P. H.; Sooley, K. A.; Sornarajah, S.; Streicher, O.; Teuben, P.; Thomas, S. W.; Tremblay, Grant R.; Turner, J. E. H.; Terrón, V.; van Kerkwijk, M. H.; de la Vega, A.; Watkins, L. L.; Weaver, B. A.; Whitmore, J. B.; Woillez, J.; Zabalza, V.; Astropy Contributors
Abstract: The Astropy Project supports and fosters the development of open-source and openly developed Python packages that provide commonly needed functionality to the astronomical community. A key element of the Astropy Project is the core package astropy, which serves as the foundation for more specialized projects and packages. In this article, we provide an overview of the organization of the Astropy project and summarize key features in the core package, as of the recent major release, version 2.0. We then describe the project infrastructure designed to facilitate and support development for a broader ecosystem of interoperable packages. We conclude with a future outlook of planned new features and directions for the broader Astropy Project. .
Magnetic reconnection in the low solar chromosphere with a more realistic radiative cooling modelNi, LeiLukin, Vyacheslav S.Murphy, Nicholas A.Lin, JunDOI: info:10.1063/1.5018351v. 25042903
Ni, Lei, Lukin, Vyacheslav S., Murphy, Nicholas A., and Lin, Jun. 2018. "Magnetic reconnection in the low solar chromosphere with a more realistic radiative cooling model." Physics of Plasmas 25:042903. https://doi.org/10.1063/1.5018351
ID: 147039
Type: article
Authors: Ni, Lei; Lukin, Vyacheslav S.; Murphy, Nicholas A.; Lin, Jun
Abstract: Magnetic reconnection is the most likely mechanism responsible for the high temperature events that are observed in strongly magnetized locations around the temperature minimum in the low solar chromosphere. This work improves upon our previous work [Ni et al., Astrophys. J. 852, 95 (2018)] by using a more realistic radiative cooling model computed from the OPACITY project and the CHIANTI database. We find that the rate of ionization of the neutral component of the plasma is still faster than recombination within the current sheet region. For low beta plasmas, the ionized and neutral fluid flows are well-coupled throughout the reconnection region resembling the single-fluid Sweet-Parker model dynamics. Decoupling of the ion and neutral inflows appears in the higher beta case with beta0=1.46 , which leads to a reconnection rate about three times faster than the rate predicted by the Sweet-Parker model. In all cases, the plasma temperature increases with time inside the current sheet, and the maximum value is above 2 ×104 K when the reconnection magnetic field strength is greater than 500 G. While the more realistic radiative cooling model does not result in qualitative changes of the characteristics of magnetic reconnection, it is necessary for studying the variations of the plasma temperature and ionization fraction inside current sheets in strongly magnetized regions of the low solar atmosphere. It is also important for studying energy conversion during the magnetic reconnection process when the hydrogen-dominated plasma approaches full ionization.
Magnetic Reconnection in Strongly Magnetized Regions of the Low Solar ChromosphereNi, LeiLukin, Vyacheslav S.Murphy, Nicholas A.Lin, JunDOI: info:10.3847/1538-4357/aa9edbv. 85295
Ni, Lei, Lukin, Vyacheslav S., Murphy, Nicholas A., and Lin, Jun. 2018. "Magnetic Reconnection in Strongly Magnetized Regions of the Low Solar Chromosphere." The Astrophysical Journal 852:95. https://doi.org/10.3847/1538-4357/aa9edb
ID: 145765
Type: article
Authors: Ni, Lei; Lukin, Vyacheslav S.; Murphy, Nicholas A.; Lin, Jun
Abstract: Magnetic reconnection in strongly magnetized regions around the temperature minimum region of the low solar atmosphere is studied by employing MHD-based simulations of a partially ionized plasma within a reactive 2.5D multi-fluid model. It is shown that in the absence of magnetic nulls in a low beta plasma, the ionized and neutral fluid flows are well-coupled throughout the reconnection region. However, non-equilibrium ionization--recombination dynamics play a critical role in determining the structure of the reconnection region, leading to much lower temperature increases and a faster magnetic reconnection rate as compared to simulations that assume plasma to be in ionization--recombination equilibrium. The rate of ionization of the neutral component of the plasma is always faster than recombination within the current sheet region even when the initial plasma beta is as high as {beta }0=1.46. When the reconnecting magnetic field is in excess of a kilogauss and the plasma beta is lower than 0.0145, the initially weakly ionized plasmas can become fully ionized within the reconnection region and the current sheet can be strongly heated to above 2.5× {10}4 K, even as most of the collisionally dissipated magnetic energy is radiated away. The Hall effect increases the reconnection rate slightly, but in the absence of magnetic nulls it does not result in significant asymmetries or change the characteristics of the reconnection current sheet down to meter scales.
Blob Formation and Ejection in Coronal Jets due to the Plasmoid and Kelvin-Helmholtz InstabilitiesNi, LeiZhang, Qing-MinMurphy, Nicholas A.Lin, JunDOI: info:10.3847/1538-4357/aa6ffev. 84127
Ni, Lei, Zhang, Qing-Min, Murphy, Nicholas A., and Lin, Jun. 2017. "Blob Formation and Ejection in Coronal Jets due to the Plasmoid and Kelvin-Helmholtz Instabilities." The Astrophysical Journal 841:27. https://doi.org/10.3847/1538-4357/aa6ffe
ID: 143318
Type: article
Authors: Ni, Lei; Zhang, Qing-Min; Murphy, Nicholas A.; Lin, Jun
Abstract: We perform 2D resistive magnetohydrodynamic simulations of coronal jets driven by flux emergence along the lower boundary. The reconnection layers are susceptible to the formation of blobs that are ejected in the jet. Our simulation with low plasma ? (Case I) shows that magnetic islands form easily and propagate upward in the jet. These islands are multithermal and thus are predicted to show up in hot channels (335 Å and 211 Å) and the cool channel (304 Å) in observations by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory. The islands have maximum temperatures of 8 MK, lifetimes of 120 s, diameters of 6 Mm, and velocities of 200 km s-1. These parameters are similar to the properties of blobs observed in extreme-ultraviolet (EUV) jets by AIA. The Kelvin-Helmholtz instability develops in our simulation with moderately high plasma ? (Case II) and leads to the formation of bright vortex-like blobs above the multiple high magnetosonic Mach number regions that appear along the jet. These vortex-like blobs can also be identified in the AIA channels. However, they eventually move downward and disappear after the high magnetosonic Mach number regions disappear. In the lower plasma ? case, the lifetime for the jet is shorter, the jet and magnetic islands are formed with higher velocities and temperatures, the current-sheet fragments are more chaotic, and more magnetic islands are generated. Our results show that the plasmoid instability and Kelvin-Helmholtz instability along the jet are both possible causes of the formation of blobs observed at EUV wavelengths.
Time-dependent Ionization in a Steady Flow in an MHD Model of the Solar Corona and WindShen, ChengcaiRaymond, John C.Mikic, ZoranLinker, Jon A.Reeves, Katharine K.Murphy, Nicholas A.DOI: info:10.3847/1538-4357/aa93f3v. 85026
Shen, Chengcai, Raymond, John C., Mikic, Zoran, Linker, Jon A., Reeves, Katharine K., and Murphy, Nicholas A. 2017. "Time-dependent Ionization in a Steady Flow in an MHD Model of the Solar Corona and Wind." The Astrophysical Journal 850:26. https://doi.org/10.3847/1538-4357/aa93f3
ID: 144807
Type: article
Authors: Shen, Chengcai; Raymond, John C.; Mikic, Zoran; Linker, Jon A.; Reeves, Katharine K.; Murphy, Nicholas A.
Abstract: Time-dependent ionization is important for diagnostics of coronal streamers and pseudostreamers. We describe time-dependent ionization calculations for a three-dimensional magnetohydrodynamic (MHD) model of the solar corona and inner heliosphere. We analyze how non-equilibrium ionization (NEI) influences emission from a pseudostreamer during the Whole Sun Month interval (Carrington rotation CR1913, 1996 August 22 to September 18). We use a time-dependent code to calculate NEI states, based on the plasma temperature, density, velocity, and magnetic field in the MHD model, to obtain the synthetic emissivities and predict the intensities of the Ly?, O VI, Mg x, and Si xii emission lines observed by the SOHO/Ultraviolet Coronagraph Spectrometer (UVCS). At low coronal heights, the predicted intensity profiles of both Ly? and O VI lines match UVCS observations well, but the Mg x and Si xii emission are predicted to be too bright. At larger heights, the O VI and Mg x lines are predicted to be brighter for NEI than equilibrium ionization around this pseudostreamer, and Si xii is predicted to be fainter for NEI cases. The differences of predicted UVCS intensities between NEI and equilibrium ionization are around a factor of 2, but neither matches the observed intensity distributions along the full length of the UVCS slit. Variations in elemental abundances in closed field regions due to the gravitational settling and the FIP effect may significantly contribute to the predicted uncertainty. The assumption of Maxwellian electron distributions and errors in the magnetic field on the solar surface may also have notable effects on the mismatch between observations and model predictions.
Review on Current Sheets in CME Development: Theories and ObservationsLin, JunMurphy, Nicholas A.Shen, ChengcaiRaymond, John C.Reeves, Katharine K.Zhong, JiayongWu, NingLi, YanDOI: info:10.1007/s11214-015-0209-0v. 194237–302
Lin, Jun, Murphy, Nicholas A., Shen, Chengcai, Raymond, John C., Reeves, Katharine K., Zhong, Jiayong, Wu, Ning, and Li, Yan. 2015. "Review on Current Sheets in CME Development: Theories and Observations." Space Science Reviews 194:237– 302. https://doi.org/10.1007/s11214-015-0209-0
ID: 140506
Type: article
Authors: Lin, Jun; Murphy, Nicholas A.; Shen, Chengcai; Raymond, John C.; Reeves, Katharine K.; Zhong, Jiayong; Wu, Ning; Li, Yan
Abstract: We introduce how the catastrophe model for solar eruptions predicted the formation and development of the long current sheet (CS) and how the observations were used to recognize the CS at the place where the CS is presumably located. Then, we discuss the direct measurement of the CS region thickness by studying the brightness distribution of the CS region at different wavelengths. The thickness ranges from 104 km to about 105 km at heights between 0.27 and 1.16 R_{?} from the solar surface. But the traditional theory indicates that the CS is as thin as the proton Larmor radius, which is of order tens of meters in the corona. We look into the huge difference in the thickness between observations and theoretical expectations. The possible impacts that affect measurements and results are studied, and physical causes leading to a thick CS region in which reconnection can still occur at a reasonably fast rate are analyzed. Studies in both theories and observations suggest that the difference between the true value and the apparent value of the CS thickness is not significant as long as the CS could be recognised in observations. We review observations that show complex structures and flows inside the CS region and present recent numerical modelling results on some aspects of these structures. Both observations and numerical experiments indicate that the downward reconnection outflows are usually slower than the upward ones in the same eruptive event. Numerical simulations show that the complex structure inside CS and its temporal behavior as a result of turbulence and the Petschek-type slow-mode shock could probably account for the thick CS and fast reconnection. But whether the CS itself is that thick still remains unknown since, for the time being, we cannot measure the electric current directly in that region. We also review the most recent laboratory experiments of reconnection driven by energetic laser beams, and discuss some important topics for future works.
Asymmetric Magnetic Reconnection in Weakly Ionized Chromospheric PlasmasMurphy, Nicholas A.Lukin, Vyacheslav S.DOI: info:10.1088/0004-637X/805/2/134v. 805134
Murphy, Nicholas A. and Lukin, Vyacheslav S. 2015. "Asymmetric Magnetic Reconnection in Weakly Ionized Chromospheric Plasmas." The Astrophysical Journal 805:134. https://doi.org/10.1088/0004-637X/805/2/134
ID: 136593
Type: article
Authors: Murphy, Nicholas A.; Lukin, Vyacheslav S.
Abstract: Realistic models of magnetic reconnection in the solar chromosphere must take into account that the plasma is partially ionized and that plasma conditions within any two magnetic flux bundles undergoing reconnection may not be the same. Asymmetric reconnection in the chromosphere may occur when newly emerged flux interacts with pre-existing, overlying flux. We present 2.5D simulations of asymmetric reconnection in weakly ionized, reacting plasmas where the magnetic field strengths, ion and neutral densities, and temperatures are different in each upstream region. The plasma and neutral components are evolved separately to allow non-equilibrium ionization. As in previous simulations of chromospheric reconnection, the current sheet thins to the scale of the neutral–ion mean free path and the ion and neutral outflows are strongly coupled. However, the ion and neutral inflows are asymmetrically decoupled. In cases with magnetic asymmetry, a net flow of neutrals through the current sheet from the weak-field (high-density) upstream region into the strong-field upstream region results from a neutral pressure gradient. Consequently, neutrals dragged along with the outflow are more likely to originate from the weak-field region. The Hall effect leads to the development of a characteristic quadrupole magnetic field modified by asymmetry, but the X-point geometry expected during Hall reconnection does not occur. All simulations show the development of plasmoids after an initial laminar phase.
The appearance, motion, and disappearance of three-dimensional magnetic null pointsMurphy, Nicholas A.Parnell, Clare E.Haynes, Andrew L.DOI: info:10.1063/1.4934929v. 22102117
Murphy, Nicholas A., Parnell, Clare E., and Haynes, Andrew L. 2015. "The appearance, motion, and disappearance of three-dimensional magnetic null points." Physics of Plasmas 22:102117. https://doi.org/10.1063/1.4934929
ID: 140555
Type: article
Authors: Murphy, Nicholas A.; Parnell, Clare E.; Haynes, Andrew L.
Abstract: While theoretical models and simulations of magnetic reconnection often assume symmetry such that the magnetic null point when present is co-located with a flow stagnation point, the introduction of asymmetry typically leads to non-ideal flows across the null point. To understand this behavior, we present exact expressions for the motion of three-dimensional linear null points. The most general expression shows that linear null points move in the direction along which the magnetic field and its time derivative are antiparallel. Null point motion in resistive magnetohydrodynamics results from advection by the bulk plasma flow and resistive diffusion of the magnetic field, which allows non-ideal flows across topological boundaries. Null point motion is described intrinsically by parameters evaluated locally; however, global dynamics help set the local conditions at the null point. During a bifurcation of a degenerate null point into a null-null pair or the reverse, the instantaneous velocity of separation or convergence of the null-null pair will typically be infinite along the null space of the Jacobian matrix of the magnetic field, but with finite components in the directions orthogonal to the null space. Not all bifurcating null-null pairs are connected by a separator. Furthermore, except under special circumstances, there will not exist a straight line separator connecting a bifurcating null-null pair. The motion of separators cannot be described using solely local parameters because the identification of a particular field line as a separator may change as a result of non-ideal behavior elsewhere along the field line.
A Lagrangian scheme for time-dependent ionization in simulations of astrophysical plasmasShen, C.Raymond, John C.Murphy, N. A.Lin, J.DOI: info:10.1016/j.ascom.2015.04.003v. 121–10
Shen, C., Raymond, John C., Murphy, N. A., and Lin, J. 2015. "A Lagrangian scheme for time-dependent ionization in simulations of astrophysical plasmas." Astronomy and Computing 12:1– 10. https://doi.org/10.1016/j.ascom.2015.04.003
ID: 140499
Type: article
Authors: Shen, C.; Raymond, John C.; Murphy, N. A.; Lin, J.
Abstract: Time-dependent ionization is important in astrophysical environments where the thermodynamical time scale is shorter than the ionization or recombination time scales. In this work, we report a FORTRAN program that performs fast non-equilibrium ionization calculations in post-processing based on hydrodynamics(HD) or magnetohydrodynamics(MHD) simulation results. Using HD or MHD simulation results, we track the movement of plasma in a Lagrangian framework, and obtain the evolutionary history of temperature and electron density. The time-dependent ionization equations are then solved by the Eigenvalue method. For any complex temperature and electron density histories, we introduce an adaptive time-step strategy to improve the computational efficiency. Our tests show that this program has advantages of high numerical stability and high accuracy. In addition, it is also easy to extend this solver to other HD and MHD simulations. This code is freely available for download from the Web.
Prevalence of small-scale jets from the networks of the solar transition region and chromosphereTian, H.DeLuca, Edward E.Cranmer, S. R.De Pontieu, B.Peter, H.Martínez-Sykora, J.Golub, L.McKillop, S.Reeves, Katharine K.Miralles, Mari PazMcCauley, P.Saar, S.Testa, P.Weber, Mark A.Murphy, N.Lemen, J.Title, A.Boerner, P.Hurlburt, N.Tarbell, T. D.Wuelser, J. P.Kleint, L.Kankelborg, C.Jaeggli, S.Carlsson, M.Hansteen, V.McIntosh, S. W.DOI: info:10.1126/science.1255711v. 3461255711
Tian, H., DeLuca, Edward E., Cranmer, S. R., De Pontieu, B., Peter, H., Martínez-Sykora, J., Golub, L., McKillop, S., Reeves, Katharine K., Miralles, Mari Paz, McCauley, P., Saar, S., Testa, P., Weber, Mark A., Murphy, N., Lemen, J., Title, A., Boerner, P., Hurlburt, N., Tarbell, T. D., Wuelser, J. P., Kleint, L., Kankelborg, C., Jaeggli, S., Carlsson, M. et al. 2014. "Prevalence of small-scale jets from the networks of the solar transition region and chromosphere." Science 346:1255711. https://doi.org/10.1126/science.1255711
ID: 131080
Type: article
Authors: Tian, H.; DeLuca, Edward E.; Cranmer, S. R.; De Pontieu, B.; Peter, H.; Martínez-Sykora, J.; Golub, L.; McKillop, S.; Reeves, Katharine K.; Miralles, Mari Paz; McCauley, P.; Saar, S.; Testa, P.; Weber, Mark A.; Murphy, N.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; Kleint, L.; Kankelborg, C.; Jaeggli, S.; Carlsson, M.; Hansteen, V.; McIntosh, S. W.
Abstract: As the interface between the Sun's photosphere and corona, the chromosphere and transition region play a key role in the formation and acceleration of the solar wind. Observations from the Interface Region Imaging Spectrograph reveal the prevalence of intermittent small-scale jets with speeds of 80 to 250 kilometers per second from the narrow bright network lanes of this interface region. These jets have lifetimes of 20 to 80 seconds and widths of ≤300 kilometers. They originate from small-scale bright regions, often preceded by footpoint brightenings and accompanied by transverse waves with amplitudes of ~20 kilometers per second. Many jets reach temperatures of at least ~105 kelvin and constitute an important element of the transition region structures. They are likely an intermittent but persistent source of mass and energy for the solar wind.
Imaging and Spectroscopic Observations of Magnetic Reconnection and Chromospheric Evaporation in a Solar FlareTian, HuiLi, GangReeves, Katharine K.Raymond, John C.Guo, FanLiu, WeiChen, BinMurphy, Nicholas A.DOI: info:10.1088/2041-8205/797/2/L14v. 797L14
Tian, Hui, Li, Gang, Reeves, Katharine K., Raymond, John C., Guo, Fan, Liu, Wei, Chen, Bin, and Murphy, Nicholas A. 2014. "Imaging and Spectroscopic Observations of Magnetic Reconnection and Chromospheric Evaporation in a Solar Flare." Astrophysical Journal Letters 797:L14. https://doi.org/10.1088/2041-8205/797/2/L14
ID: 133417
Type: article
Authors: Tian, Hui; Li, Gang; Reeves, Katharine K.; Raymond, John C.; Guo, Fan; Liu, Wei; Chen, Bin; Murphy, Nicholas A.
Abstract: Magnetic reconnection is believed to be the dominant energy release mechanism in solar flares. The standard flare model predicts both downward and upward outflow plasmas with speeds close to the coronal Alfvén speed. Yet, spectroscopic observations of such outflows, especially the downflows, are extremely rare. With observations of the newly launched Interface Region Imaging Spectrograph (IRIS), we report the detection of a greatly redshifted (~125 km s-1 along the line of sight) Fe XXI 1354.08 Å emission line with a ~100 km s-1 nonthermal width at the reconnection site of a flare. The redshifted Fe XXI feature coincides spatially with the loop-top X-ray source observed by RHESSI. We interpret this large redshift as the signature of downward-moving reconnection outflow/hot retracting loops. Imaging observations from both IRIS and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory also reveal the eruption and reconnection processes. Fast downward-propagating blobs along these loops are also found from cool emission lines (e.g., Si IV, O IV, C II, Mg II) and images of AIA and IRIS. Furthermore, the entire Fe XXI line is blueshifted by ~260 km s-1 at the loop footpoints, where the cool lines mentioned above all exhibit obvious redshift, a result that is consistent with the scenario of chromospheric evaporation induced by downward-propagating nonthermal electrons from the reconnection site.
The JOVIAL Project for Jovian SeismologySchmider, F. X.Appourchaux, T.Gaulme, P.Guillot, T.Sato, B.Murphy, N.Daban, J. B.Gay, J.Soulat, L.Baudin, F.Boumier, P.Ollivier, M.Bordé. P.Jackiewicz, J.Ida, S.Showman, A. P.Jain, K.Tripathy, S. C.Hill, F.Leibacher, J. W.Pevtsov, A. A.v. 478119
Schmider, F. X., Appourchaux, T., Gaulme, P., Guillot, T., Sato, B., Murphy, N., Daban, J. B., Gay, J., Soulat, L., Baudin, F., Boumier, P., Ollivier, M., Bordé. P., Jackiewicz, J., Ida, S., Showman, A. P., Jain, K., Tripathy, S. C., Hill, F., Leibacher, J. W., and Pevtsov, A. A. 2013. "The JOVIAL Project for Jovian Seismology." In , , 119.
ID: 120742
Type: conference
Authors: Schmider, F. X.; Appourchaux, T.; Gaulme, P.; Guillot, T.; Sato, B.; Murphy, N.; Daban, J. B.; Gay, J.; Soulat, L.; Baudin, F.; Boumier, P.; Ollivier, M.; Bordé. P.; Jackiewicz, J.; Ida, S.; Showman, A. P.; Jain, K.; Tripathy, S. C.; Hill, F.; Leibacher, J. W.; Pevtsov, A. A.
Non-equilibrium Ionization Modeling of the Current Sheet in a Simulated Solar EruptionShen, ChengcaiReeves, Katharine K.Raymond, John C.Murphy, Nicholas A.Ko, Yuan-KuenLin, JunMikic, ZoranLinker, Jon A.DOI: info:10.1088/0004-637X/773/2/110v. 773110
Shen, Chengcai, Reeves, Katharine K., Raymond, John C., Murphy, Nicholas A., Ko, Yuan-Kuen, Lin, Jun, Mikic, Zoran, and Linker, Jon A. 2013. "Non-equilibrium Ionization Modeling of the Current Sheet in a Simulated Solar Eruption." The Astrophysical Journal 773:110. https://doi.org/10.1088/0004-637X/773/2/110
ID: 116798
Type: article
Authors: Shen, Chengcai; Reeves, Katharine K.; Raymond, John C.; Murphy, Nicholas A.; Ko, Yuan-Kuen; Lin, Jun; Mikic, Zoran; Linker, Jon A.
Abstract: The current sheet that extends from the top of flare loops and connects to an associated flux rope is a common structure in models of coronal mass ejections (CMEs). To understand the observational properties of CME current sheets, we generated predictions from a flare/CME model to be compared with observations. We use a simulation of a large-scale CME current sheet previously reported by Reeves et al. This simulation includes ohmic and coronal heating, thermal conduction, and radiative cooling in the energy equation. Using the results of this simulation, we perform time-dependent ionization calculations of the flow in a CME current sheet and construct two-dimensional spatial distributions of ionic charge states for multiple chemical elements. We use the filter responses from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory and the predicted intensities of emission lines to compute the count rates for each of the AIA bands. The results show differences in the emission line intensities between equilibrium and non-equilibrium ionization. The current sheet plasma is underionized at low heights and overionized at large heights. At low heights in the current sheet, the intensities of the AIA 94 Å and 131 Å channels are lower for non-equilibrium ionization than for equilibrium ionization. At large heights, these intensities are higher for non-equilibrium ionization than for equilibrium ionization inside the current sheet. The assumption of ionization equilibrium would lead to a significant underestimate of the temperature low in the current sheet and overestimate at larger heights. We also calculate the intensities of ultraviolet lines and predict emission features to be compared with events from the Ultraviolet Coronagraph Spectrometer on the Solar and Heliospheric Observatory, including a low-intensity region around the current sheet corresponding to this model.
Numerical experiments on magnetic reconnection in solar flare and coronal mass ejection current sheetsMei, Z.Shen, C.Wu, N.Lin, J.Murphy, N. A.Roussev, I. I.DOI: info:10.1111/j.1365-2966.2012.21625.xv. 4252824–2839
Mei, Z., Shen, C., Wu, N., Lin, J., Murphy, N. A., and Roussev, I. I. 2012. "Numerical experiments on magnetic reconnection in solar flare and coronal mass ejection current sheets." Monthly Notices of the Royal Astronomical Society 425:2824– 2839. https://doi.org/10.1111/j.1365-2966.2012.21625.x
ID: 113673
Type: article
Authors: Mei, Z.; Shen, C.; Wu, N.; Lin, J.; Murphy, N. A.; Roussev, I. I.
Abstract: Magnetic reconnection plays a critical role in energy conversion during solar eruptions. This paper presents a set of magnetohydrodynamic experiments for the magnetic reconnection process in a current sheet (CS) formed in the wake of the rising flux rope. The eruption results from the loss of equilibrium in a magnetic configuration that includes a current-carrying flux rope, representing a pre-existing filament. In order to study the fine structure and micro processes inside the CS, mesh refinement is used to reduce the numerical diffusion. We start with a uniform, explicitly defined resistivity which results in a Lundquist number S = 104 in the vicinity of CS. The use of mesh refinement allows the simulation to capture high-resolution features such as plasmoids from the tearing mode and plasmoid instability regions of turbulence and slow-mode shocks. Inside the CS, magnetic reconnection goes through the Sweet-Parker and the fractal stages, and eventually displays a time-dependent Petschek pattern. Our results support the concept of fractal reconnection suggested by Shibata et al. and Shibata & Tanuma, and also suggest that the CS evolves through Sweet-Parker reconnection prior to the fast reconnection stage. For the first time, the detailed features and/or fine structures inside the coronal mass ejection/flare CS in the eruption were investigated in this work.
Asymmetric Magnetic Reconnection in Solar Flare and Coronal Mass Ejection Current SheetsMurphy, N. A.Miralles, Mari PazPope, C. L.Raymond, John C.Winter, H. D.Reeves, Katharine K.Seaton, D. B.van Ballegooijen, Adriaan A.Lin, J.DOI: info:10.1088/0004-637X/751/1/56v. 75156
Murphy, N. A., Miralles, Mari Paz, Pope, C. L., Raymond, John C., Winter, H. D., Reeves, Katharine K., Seaton, D. B., van Ballegooijen, Adriaan A., and Lin, J. 2012. "Asymmetric Magnetic Reconnection in Solar Flare and Coronal Mass Ejection Current Sheets." The Astrophysical Journal 751:56. https://doi.org/10.1088/0004-637X/751/1/56
ID: 111709
Type: article
Authors: Murphy, N. A.; Miralles, Mari Paz; Pope, C. L.; Raymond, John C.; Winter, H. D.; Reeves, Katharine K.; Seaton, D. B.; van Ballegooijen, Adriaan A.; Lin, J.
Abstract: We present two-dimensional resistive magnetohydrodynamic simulations of line-tied asymmetric magnetic reconnection in the context of solar flare and coronal mass ejection current sheets. The reconnection process is made asymmetric along the inflow direction by allowing the initial upstream magnetic field strengths and densities to differ, and along the outflow direction by placing the initial perturbation near a conducting wall boundary that represents the photosphere. When the upstream magnetic fields are asymmetric, the post-flare loop structure is distorted into a characteristic skewed candle flame shape. The simulations can thus be used to provide constraints on the reconnection asymmetry in post-flare loops. More hard X-ray emission is expected to occur at the footpoint on the weak magnetic field side because energetic particles are more likely to escape the magnetic mirror there than at the strong magnetic field footpoint. The footpoint on the weak magnetic field side is predicted to move more quickly because of the requirement in two dimensions that equal amounts of flux must be reconnected from each upstream region. The X-line drifts away from the conducting wall in all simulations with asymmetric outflow and into the strong magnetic field region during most of the simulations with asymmetric inflow. There is net plasma flow across the X-line for both the inflow and outflow directions. The reconnection exhaust directed away from the obstructing wall is significantly faster than the exhaust directed toward it. The asymmetric inflow condition allows net vorticity in the rising outflow plasmoid which would appear as rolling motions about the flux rope axis.
Transition Region Emission from Solar Flares during the Impulsive PhaseJohnson, H.Raymond, John C.Murphy, Nicholas A.Giordano, S.Ko, Y. K.Ciaravella, A.Suleiman, RaidDOI: info:10.1088/0004-637X/735/2/70v. 73570
Johnson, H., Raymond, John C., Murphy, Nicholas A., Giordano, S., Ko, Y. K., Ciaravella, A., and Suleiman, Raid. 2011. "Transition Region Emission from Solar Flares during the Impulsive Phase." The Astrophysical Journal 735:70. https://doi.org/10.1088/0004-637X/735/2/70
ID: 101628
Type: article
Authors: Johnson, H.; Raymond, John C.; Murphy, Nicholas A.; Giordano, S.; Ko, Y. K.; Ciaravella, A.; Suleiman, Raid
Abstract: There are relatively few observations of UV emission during the impulsive phases of solar flares, so the nature of that emission is
poorly known. Photons produced by solar flares can resonantly scatter off atoms and ions in the corona. Based on off-limb measurements by the Solar and Heliospheric Observatory/Ultraviolet Coronagraph Spectrometer, we derive the O VI λ 1032 luminosities for 29 flares during the impulsive phase and the Lyα luminosities of 5 flares, and we compare them with X-ray luminosities from GOES measurements. The upper transition region and lower transition region luminosities of the events observed are comparable. They are also comparable to the luminosity of the X-ray emitting gas at the beginning of the flare, but after 10-15 minutes the X-ray luminosity usually dominates. In some cases, we can use Doppler dimming to estimate flow speeds of the O VI emitting gas, and five events show speeds in the 40-80 km s-1 range. The O VI emission could originate in gas evaporating to fill the X-ray flare loops, in heated chromospheric gas at the footpoints, or in heated prominence material in the coronal mass ejection. All three sources may contribute in different events or even in a single event, and the relative timing of UV and X-ray brightness peaks, the flow speeds, and the total O VI luminosity favor each source in one or more events.
Plasma Heating During a Coronal Mass Ejection Observed By the Solar and Heliospheric ObservatoryMurphy, Nicholas A.Raymond, John C.Korreck, K. E.DOI: info:10.1088/0004-637X/735/1/17v. 73517
Murphy, Nicholas A., Raymond, John C., and Korreck, K. E. 2011. "Plasma Heating During a Coronal Mass Ejection Observed By the Solar and Heliospheric Observatory." The Astrophysical Journal 735:17. https://doi.org/10.1088/0004-637X/735/1/17
ID: 101631
Type: article
Authors: Murphy, Nicholas A.; Raymond, John C.; Korreck, K. E.
Abstract: We perform a time-dependent ionization analysis to constrain plasma heating requirements during a fast partial halo coronal mass ejection (CME) observed on 2000 June 28 by the Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory (SOHO). We use two methods to derive densities from the UVCS measurements, including a density sensitive O V line ratio at 1213.85 and 1218.35 Å, and radiative pumping of the O VI λλ1032, 1038 doublet by chromospheric emission lines. The most strongly constrained feature shows cumulative plasma heating comparable to or greater than the kinetic energy, while features observed earlier during the event show plasma heating of order or less than the kinetic energy. SOHO Michelson Doppler Imager observations are
used to estimate the active region magnetic energy. We consider candidate plasma heating mechanisms and provide constraints when possible. Because this CME was associated with a relatively weak flare, the contribution from flare energy (e.g., through thermal conduction or energetic particles) is probably small; however, the flare may have been partially behind the limb. Wave heating by photospheric motions requires heating rates to be significantly larger than those previously inferred for coronal holes, but the eruption itself could drive waves that heat the plasma. Heating by small-scale reconnection in the flux rope or by the CME current sheet is not significantly constrained. UVCS line widths suggest that turbulence must be replenished continually and dissipated on timescales shorter than the propagation time in order to be an intermediate step in CME heating.
Magnetic reconnection X-line retreat associated with dipolarization of the Earth's magnetosphereOka, M.Phan, T. -DEastwood, J. P.Angelopoulos, V.Murphy, N. A.Øieroset, M.Miyashita, Y.Fujimoto, M.McFadden, J.Larson, D.DOI: info:10.1029/2011GL049350v. 3820105
Oka, M., Phan, T. -D, Eastwood, J. P., Angelopoulos, V., Murphy, N. A., Øieroset, M., Miyashita, Y., Fujimoto, M., McFadden, J., and Larson, D. 2011. "Magnetic reconnection X-line retreat associated with dipolarization of the Earth's magnetosphere." Geophysical Research Letters 38:20105. https://doi.org/10.1029/2011GL049350
ID: 108038
Type: article
Authors: Oka, M.; Phan, T. -D; Eastwood, J. P.; Angelopoulos, V.; Murphy, N. A.; Øieroset, M.; Miyashita, Y.; Fujimoto, M.; McFadden, J.; Larson, D.
Abstract: Magnetic reconnection is the key process of plasma transport in the Earth's magnetotail. The ‘X-line’ where magnetic field lines reconnect often moves away from the Earth. However, the precise cause of the X-line motion remains unclear. Here we present data from five THEMIS probes positioned along the Sun-Earth line and show that a tailward retreat motion of the X-line (detected by the outermost probe P1) occurred when the dipolarized inner magnetosphere started to return to a more stretched, tail-like configuration (observed by the inner probes P3, P4, and P5). At an intermediate location (P2), the total pressure was increasing. These observations are consistent with the idea that the pressure increase in the inner magnetosphere eventually causes the X-line to retreat tailward.