BREAKOUT CORONAL MASS EJECTION OR STREAMER BLOWOUT: THE BUGLE EFFECT

Abstract

We present three-dimensional numerical magnetohydrodynamic (MHD) simulations of coronal mass ejections (CMEs) initiated by the breakout mechanism. The initial steady state consists of a bipolar active region embedded in the solar wind. The field orientation of the active region is opposite to that of the overarching helmet streamer, so that this pre-eruptive region consists of three arcades with a magnetic null line on the leading edge of the central arcade. By applying footpoint motion near the polarity inversion line of the central arcade, the breakout reconnection is turned on. During the eruption, the plasma in front of the breakout arcade gets swept up. The latter effect causes a pre-event swelling of the streamer. The width of the helmet streamer increases in time and follows a bugle pattern. In this paper, we will demonstrate that if this pre-event streamer swelling is insufficient, reconnection on the sides of the erupting breakout arcade/flux rope sets in. This will ultimately disconnect the helmet top, resulting in a streamer blowout CME. On the other hand, if this pre-event swelling is effective enough, the breakout reconnection will continue all the way to the top of the helmet streamer. The breakout mechanisms will then succeed in creating a breakout CME.