Study of Multiple Coronal Mass Ejections at Solar Minimum Conditions

The aim of this work is to provide a physical explanation for the genesis of multiple coronal mass ejections (CMEs) in an asymmetric coronal field configuration. We analyze STEREO observations of a multiple eruption and compare the results from the data analysis with predictions provided by magnetohydrodynamic (MHD) simulations. To this end, the multiple CMEs (MCMEs) observed on 21 -aEuro parts per thousand 22 September 2009 were selected. Both eruptions originated from the same source region and showed approximately the same latitudinal deflection, by more than 15 degrees, toward the heliospheric current sheet (HCS) during their propagation in the COR1 field of view. Numerical MHD simulations of the MCMEs have been performed, starting from an asymmetric coronal field configuration that mimics the potential field source surface extrapolation for 21 September 2009. The results demonstrate that, by shearing the footpoints at the base of the southern arcade, we were able to reproduce the observed dynamics of the MCMEs. Both CMEs are deflected toward the HCS due to an imbalance in the magnetic pressure and tension forces; the global field strength turns out to be a crucial parameter in order to release two subsequent eruptions, and hence to reproduce the observed evolution.