Solar Atmospheric Dynamic Coupling Due to Shear Motions Driven by the Lorentz Force

Abstract

Recent theoretical and numerical works have shown that shearing motions observed during magnetic flux emergence are driven by the Lorentz force. The Lorentz force results from the nonuniform expansion of the magnetic field in a highly pressure-stratified atmosphere. This deformation of the flux system causes the axial component of the field to become weaker (along field lines) in the corona than in the lower atmosphere, which produces the shearing Lorentz force. The shear flows result in the magnetic field being drawn parallel to the polarity inversion lines of active regions as observed at the photosphere and in filaments. In order to arrive at an equilibrium state after flux emergence, the axial field must evolve to be constant along field lines. This nonlocal requirement for force balance results in a coupling by shear flows that act to equilibrate the axial magnetic field. This paper will elaborate on the dynamic coupling such shearing flows cause between the layers of the solar atmosphere. This coupling occurs by way of self-organized flows that transport magnetic flux and energy from below the photosphere into the corona. This work explains how coronal magnetic fields become energized to produce coronal mass ejections and two-ribbon flares. Subject headingg s: MHD-Sun: coronal mass ejections (CMEs)