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Ionic Composition Structure of Coronal Mass Ejections in Axisymmetric Magnetohydrodynamic Models  

Benjamin Lynch   Submitted: 2011-07-26 10:05

We present the ionic charge state composition structure derived from axisymmetric MHD simulations of coronal mass ejections (CMEs), initiated via the flux-cancellation and magnetic breakout mechanisms. The flux-cancellation CME simulation is run on the Magnetohydrodynamics-on-A-Sphere code developed at Predictive Sciences, Inc., and the magnetic breakout CME simulation is run on ARC7 developed at NASA GSFC. Both MHD codes include field-aligned thermal conduction, radiative losses, and coronal heating terms which make the energy equations sufficient to calculate reasonable temperatures associated with the steady-state solar wind and model the eruptive flare heating during CME formation and eruption. We systematically track a grid of Lagrangian plasma parcels through the simulation data and calculate the coronal density and temperature history of the plasma in and around the CME magnetic flux ropes. The simulation data are then used to integrate the continuity equations for the ionic charge states of several heavy ion species under the assumption that they act as passive tracers in the MHD flow. We construct two-dimensional spatial distributions of commonly measured ionic charge state ratios in carbon, oxygen, silicon, and iron that are typically elevated in interplanetary coronal mass ejection (ICME) plasma. We find that the slower CME eruption has relatively enhanced ionic charge states and the faster CME eruption shows basically no enhancement in charge states—which is the opposite trend to what is seen in the in situ ICME observations. The primary cause of the difference in the ionic charge states in the two simulations is not due to the different CME initiation mechanisms per se. Rather, the difference lies in their respective implementation of the coronal heating which governs the steady-state solar wind, density and temperature profiles, the duration of the connectivity of the CME to the eruptive flare current sheet, and the contribution of the flare-heated plasma associated with the reconnection jet outflow into the ejecta. Despite the limitations inherent in the first attempt at this novel procedure, the simulation results provide strong evidence in support of the conclusion that enhanced heavy ion charge states within CMEs are a direct consequence of flare heating in the low corona. We also discuss future improvements through combining numerical CME modeling with quantitative ionic charge state calculations.

Authors: B. J. Lynch, A. A. Reinard, T. Mulligan, K. K. Reeves, C. E. Rakowski, J. C. Allred, Y. Li, J. M. Laming, P. J. MacNeice, and J. A. Linker

Publication Status: ApJ, 740, 112
Last Modified: 2011-10-04 15:42
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Sun to 1 AU propagation and evolution of a slow streamer-blowout coronal mass ejection  

Benjamin Lynch   Submitted: 2010-03-25 00:37

We present a comprehensive analysis of the evolution of the classic, slow streamer-blowout CME of 1 June 2008 observed by the STEREO twin spacecraft to infer relevant properties of the pre-eruption source region which includes a substantial portion of the coronal helmet streamer belt. The CME was directed ∼40◦ East of the Sun-Earth line and the Heliospheric Imager observations are consistent with the CME propagating essentially radially to 1 AU. The elongation-time J-map constructed from the STEREO-A HI images tracks the arrival of two density peaks that bound the magnetic flux rope ICME seen at STEREO-B on 6 June 2008. From the STEREO-A elongation-time plots we measure the ICME flux rope radial size Rc(t) and find it well approximated by the constant expansion value Vexp = 24.5 km s-1 obtained from the STEREO-B declining velocity profile within the magnetic cloud. The flux rope spatial orientation, determined by forward modeling fits to the STEREO COR2 and HI1 data, approaches the observed 1 AU flux rope orientation and suggests large-scale rotation during propagation, as predicted by recent numerical simulations. We compare the ICME flux content to the PFSS model coronal field for Carrington Rotation 2070 and find sufficient streamer belt flux to account for the observed ICME poloidal/twist flux if reconnection during CME initiation process is responsible for the conversion of overlying field into the flux rope twist component in the standard fashion. However, the PFSS model field cannot account for the ICME toroidal/axial flux component. We estimate the field strength of the pre-eruption sheared/axial component in the low corona and the timescales required to accumulate this energized pre-eruption configuration via differential rotation and flux cancellation by supergranular diffusion at the polarity inversion line. We show that both mechanisms are capable of generating the desired shear component over time periods of roughly 1-2 months. We discuss the implications for slow streamer-blowout CMEs arising as a natural consequence of the corona?s re-adjustment to the long term evolutionary driving of the photospheric fields.

Authors: B. J. Lynch, Y. Li, A. F. R. Thernisien, E. Robbrecht, G. H. Fisher, J. G. Luhmann, and A. Vourlidas

Publication Status: J. Geophysical Research, Vol. 115, A07106, doi:10.1029/2009JA015099
Last Modified: 2010-07-21 17:23
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Reconnection-Driven Dynamics of Coronal-Hole Boundaries  

Benjamin Lynch   Submitted: 2009-12-04 18:54

We investigate the effect of magnetic reconnection on the boundary between open and closed magnetic field in the solar corona. The magnetic topology for our numerical study consists of a global dipole that gives rise to polar coronal holes and an equatorial streamer belt, and a smaller active-region bipole embedded inside the closed-field streamer belt. The initially potential magnetic field is energized by a rotational motion at the photosphere that slowly twists the embedded-bipole flux. Due to the applied stress, the bipole field expands outward and reconnects with the surrounding closed flux, eventually tunneling through the streamer boundary and encountering the open flux of the coronal hole. The resulting interchange reconnection between closed and open field releases the magnetic twist and free energy trapped inside the bipole onto open field lines, where they freely escape into the heliosphere along with the entrained closed-field plasma. Thereafter, the bipole field relaxes and reconnects back down into the interior of the streamer belt. Our simulation shows that the detailed properties of magnetic reconnection can be crucial to the coronal magnetic topology, which implies that both potential-field source-surface and quasi-steady magnetohydrodynamic models may often be an inadequate description of the corona and solar wind. We discuss the implications of our results for understanding the dynamics of the boundary between open and closed field on the Sun and the origins of the slow wind.

Authors: J. K. Edmondson, B. J. Lynch, S. K. Antiochos, C. R. DeVore and T. H. Zurbuchen
Projects: None

Publication Status: published 2009 ApJ vol. 707 pg.1427-1437, doi: 10.1088/0004-637X/707/2/1427
Last Modified: 2009-12-07 10:35
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Abstracts by Author
Ionic Composition Structure of Coronal Mass Ejections in Axisymmetric Magnetohydrodynamic Models
Sun to 1 AU propagation and evolution of a slow streamer-blowout coronal mass ejection
Reconnection-Driven Dynamics of Coronal-Hole Boundaries

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