Ultrahigh-resolution model of a breakout CME embedded in the solar wind

Abstract

Aims. We investigate the effect of a background solar wind on breakout coronal mass ejections, in particular, the effect on the different current sheets and the flux rope formation process. Methods. We obtained numerical simulation results by solving the magnetohydrodynamics equations on a 2.5D (axisymmetric) stretched grid. Ultrahigh spatial resolution is obtained by applying a solution adaptive mesh refinement scheme by increasing the grid resolution in regions of high electrical current, that is, by focussing on the maximum resolution of the current sheets that are forming. All simulations were performed using the same initial base grid and numerical schemes; we only varied the refinement level. Results. A background wind that causes a surrounding helmet streamer has been proven to have a substantial effect on the current sheets that are forming and thus on the dynamics and topology of the breakout release process. Two distinct ejections occur: first, the top of the helmet streamer detaches, and then the central arcade is pinched off behind the top of the helmet streamer. This is different from the breakout scenario that does not take the solar wind into account, where only the central arcade is involved in the eruption. In the new ultrahigh-resolution simulations, small-scale structures are formed in the lateral current sheets, which later merge with the helmet streamer or reconnect with the solar surface. We find that magnetic reconnections that occur at the lateral breakout current sheets deliver the major kinetic energy contribution to the eruption and not the reconnection at the so-called flare current sheet, as was seen in the case without background solar wind.