Numerical simulations of homologous coronal mass ejections in the solar wind

¹ Centre for Plasma-Astrophysics, K. U. Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium e-mail: alexander.soenen@wis.kuleuven.be
² Leuven Mathematical Modeling & Computational Science Research Center (LMCC), Belgium
³ Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands
⁴ Space Physics Research Laboratory, University of Michigan, MI 48109, USA

Received: 19 February 2009
Accepted: 7 May 2009

Abstract

Context. Coronal mass ejections (CMEs) are enormous expulsions of magnetic flux and plasma from the solar corona. Most scientists agree that a coronal mass ejection is the sudden release of magnetic free energy stored in a strongly stressed field. However, the exact reason for this sudden release is still highly debated.

Aims. In an initial multiflux system in steady state equilibrium, containing a pre-eruptive region consisting of three arcades with alternating magnetic flux polarity, we study the initiation and early evolution properties of a sequence of CMEs by shearing a region slightly larger than the central arcade.

Methods. We solve the ideal magnetohydrodynamics (MHD) equations in an axisymmetrical domain from the solar surface up to 30 . The ideal MHD equations are advanced in time over a non uniform grid using a modified version of the Versatile Advection Code (VAC).

Results. By applying shearing motions on the solar surface, the magnetic field is energised and multiple eruptions are obtained. Magnetic reconnection first opens the overlying field and two new reconnections sites set in on either side of the central arcade. After the disconnection of the large helmet top, the system starts to restore itself but cannot return to its original configuration as a new arcade has already started to erupt. This process then repeats itself as we continue shearing.

Conclusions. The simulations reported in the present paper, demonstrate the ability to obtain a sequence of CMEs by shearing a large region of the central arcade or by shearing a region that is only slightly larger than the central arcade. We show, be it in an axisymmetric configuration, that the breakout model can not only lead to confined eruptions but also to actual coronal mass ejections provided the model includes a realistic solar wind model.