3-DIMENSIONAL STRUCTURE OF CORONAL MASS EJECTIONS

Numerical solutions of the MHD equations are used to examine the three-dimensional structure of coronal mass ejections (CMEs). The initial atmosphere consists of a streamer belt at the equator, which is characteristic of coronal conditions near solar minimum. A finite azimuthal portion of the streamer belt is then disrupted by the emergence of new magnetic flux. The CME forms as the corona adjusts to accommodate the new flux. The numerical solution in a meridional plane centered over the region of newly emerged flux has features similar to those computed in previous two-dimensional simulations. The primary result of this study is that the CME is shaped more like an arcade with an axis parallel to the equator than like a bubble. This characteristic arcade shape occurs both in the density distribution in meridional and azimuthal planes and in the integrated white-light brightness in meridional and polar views. By examining the brightness change due to the CME it is found that the CME in a meridional projection as viewed from the Earth has the same loop shape even if the CME originates almost directly in front of or behind the Sun. It appears dimmer as it occurs further from the limb with a reduction in the maximum brightness of less than 30% as the CME moves from the limb to 45-degrees away from it. The peak brightness in a polar view is about 65% less than that in a meridional projection when the CME is at the limb.