PLASMA DYNAMICS OF MAGNETIC FLUX INJECTION IN THE SOLAR ATMOSPHERE

摘要

A computational analysis of magnetic flux injection from the solar photosphere into the solar chromosphere and corona is presented. The model is one-dimensional and describes the evolution of the plasma and neutrals in the vertical x-direction; the magnetic field is assumed to be unidirectional in the horizontal plane. The initial magnetic field profile is a step function (a magnetic piston): B = B_0 + ΔB for x ≤ x_0 and B = B_0 for x > x_0. The field is then allowed to relax self-consistently for t > 0 and x > x_(x_0): a shock is launched followed by the relaxation of the magnetic piston. Simulation results are presented for different initial positions x_0 of the field jump in the chromosphere. When the piston (ΔB ～ tens of gauss) is very low in the chromosphere, a weak shock is launched that results in upward plasma and neutral velocities V approx= few km s~(-1) in the upper chromosphere and corona; the plasma and neutrals only attain velocities V approx= tens of m s~(-1) in the lower chromosphere. A quasi-steady state follows, and the piston does not relax significantly because the pressure change across the magnetic piston is small. When the piston is initiated in the upper chromosphere, a stronger shock is launched into the corona; plasma and neutral velocities V approx= tens of km s~(-1) are generated. Subsequently, the magnetic field piston relaxes and penetrates the transition layer into the corona; the upward velocities are V approx= hundreds of km s~(-1). At the same time, plasma and neutrals are being swept into the corona.