NUMERICAL MODELING OF CORONAL MASS EJECTIONS BASED ON VARIOUS PRE-EVENT MODEL ATMOSPHERES

We examine how the initial state (pre-event corona) affects the numeri cal MHD simulation for a coronal mass ejection (CME). Earlier simulati ons based on a pre-event corona with a homogeneous density and tempera ture distribution at the lower boundary (i.e., solar surface) have bee n used to analyze the role of streamer properties in determining the c haracteristics of loop-like transients. The present paper extends thes e studies to show how a broader class of global coronal properties lea ds not only to different types of CMEs, but also modifies the adjacent quiet corona and/or coronal holes. We consider four pre-event coronal cases: (1) constant boundary conditions and a polytropic gas with gam ma = 1.05; (2) non-constant (latitude dependent) boundary conditions a nd a polytropic gas withy = 1.05; (3) constant boundary conditions wit h a volumetric energy source and gamma = 1.67; (4) non-constant (latit ude dependent) boundary conditions with a volumetric energy source and gamma = 1.67. In all models, the pre-event magnetic fields separate t he corona into closed field regions (streamers) and open field regions . The CME's initiation is simulated by introducing at the base of the corona, within the streamer region, a standard pressure pulse and velo city change. Boundary values are determined using MHD characteristic t heory. The simulations show how different CMEs, including loop-like tr ansients, clouds and bright rays, might occur. There are significant n ew features in comparison to published results. We conclude that the p re-event corona is a crucial factor in dictating CMEs properties.