Formation of fast shocks by magnetic reconnection in the solar corona

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Title:	Formation of fast shocks by magnetic reconnection in the solar corona
Authors:	Hsieh,MH;Tsai,CL;Ma,ZW;Lee,LC
Contributors:	太空科學研究所
Keywords:	RIEMANN PROBLEM;INTERMEDIATE SHOCKS;LOOP DYNAMICS;RE-CONNEXION;SLOW SHOCKS;MODELS;SIMULATIONS;CONSTRAINTS;MECHANISM;COMPUTER
Date:	2009
Issue Date:	2010-06-29 18:37:42 (UTC+8)
Publisher:	中央大學
Abstract:	Reconnections of magnetic fields over the solar surface are expected to generate abundant magnetohydrodynamic (MHD) discontinuities and shocks, including slow shocks and rotational discontinuities. However, the generation of fast shocks by magnetic reconnection process is relatively not well studied. In this paper, magnetic reconnection in a current sheet is studied based on two-dimensional resistive MHD numerical simulations. Magnetic reconnections in the current sheet lead to the formation of plasma jets and plasma bulges. It is further found that the plasma bulges, the leading part of plasma jets, in turn lead to the generation of fast shocks on flanks of the bulges. The simulation results show that during the magnetic reconnection process, the plasma forms a series of structures: plasma jets, plasma bulges, and fast shocks. As time increases, the bulges spread out along the current sheet (+/- z direction) and the fast shocks move just ahead of the bulges. The effects of initial parameters rho(s)/rho(m), beta(infinity), and t(rec) on the fast shock generation are also examined, where rho(s)/rho(m) is the ratio of plasma densities on two sides of the initial current sheet, beta(infinity) = P-infinity/(B-infinity(2)/2 mu(0)), P-infinity is the plasma pressure and B-infinity is the magnetic field magnitude far from the current sheet, and t(rec) is the reconnection duration. In the asymmetric case with rho(s)/rho(m) = 2, beta(infinity) = 0.01 and t(rec) = 1000, the maximum Alfven Mach number of fast shocks (M-A1 (max)) is M-A1 max congruent to 1.1, where M-A1 = V-n1/V-A1, and V-n1 and V-A1 are, respectively, the normal upstream fluid velocity and the upstream Alfven speed in the fast shocks frame. As the density ratio rho(s)/rho(m) (=1-8) and plasma beta beta(infinity) (=0.0001-1) increase, M-A1 max varies slightly. For the case with a large plasma beta beta(infinity) (=5), the fast shock is very weak. As the reconnection duration t(rec) increases, the bulges lead to generation of fast shocks with a higher M-A1 max. The present results can be applied to the mechanism of coronal heating by fast shocks. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3212889]
Relation:	PHYSICS OF PLASMAS
Appears in Collections:	[Graduate Institute of Space Science] journal & Dissertation

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