Shock And Discontinuity Formation In The Front Of An Expanding Coronal Arcade In Two-Fluid Simulations

There exists multitudes of observational evidence that sunspots,coronal mass ejec-tions,coronal heating,and other solar atmospheric phenomena are closely related to expanding magnetic coronal loops.The present thesis investigates the dynamic evolution of an expanding coronal magnetic arcade associated with footpoint shearing motions by an ideal two-fluid(electron-ion)code.The two-fluid numerical simula-tions produce conspicuous differences compared to earlier MHD simulations beyond the inner arcade region.The decoupling motion between electrons and heavier ions during the arcade expansion induces a growing charge separation and strong electric field in the front of the expanding arcade.The presence of this electric field provides an additional force,along with the magnetic and thermal pressures,that drive the growth of an outwardly expanding wave that steepens into a propagating disconti-nuity in the plasma and magnetic field.The propagation speed of the discontinuity eventually exceeds the local phase velocity of the MHD fast mode and becomes a per-pendicular fast-like shock.There is significant heating at the shock due to adiabatic compression with preferential heating of the ion fluid also being observed.In addition,parameter tests indicate that(1)the propagation speed of the shock before exiting the inner arcade is independent of the maximum shear speed;(2)slower shearing speeds produce weaker shocks with weaker adiabatic heating;(3)the ion to elec-tron mass ratio,mi/me,impacts the strength of the charge separation linearly,but has a moderate effect on the propagation speed;and(4)the normalized value of the ion inertial length does not affect the formation and the speed of the shock as a whole.