EMERGENCE OF SOLAR MAGNETIC-FLUX FROM THE CONVECTION ZONE INTO THE PHOTOSPHERE AND CHROMOSPHERE

Using a two-dimensional magnetohydrodynamic (MHD) code, we study the nonlinear dynamics of solar magnetic flux emerging from the convection zone into the photosphere and chromosphere. An isolated horizontal magnetic flux with β ≃ 4 is initially located in a convectively unstable layer (solar convection zone) beneath a two-temperature layered atmosphere (solar corona-chromosphere/photosphere). We assume ideal MHD, except in the photosphere where we employ an approximate form for radiative cooling. The combined effects of convection and magnetic buoyancy carry the magnetic flux from the convection zone into the photosphere, whereupon it then expands through the photosphere and chromosphere. Gas slides down the expanding loop, resulting in its evacuation and subsequent rise due to enhanced magnetic buoyancy. Initially weak convection zone magnetic flux (B ≃ 600 G) is amplified up to ≥ 1000 G after emerging into the photosphere by the convective collapse of the flux tube triggered by the downflow along the tube. The resulting velocity fields are similar to those observed in arch filament systems.