Magnetic Topology of the Sympathetic CMEs Observed on 27 July 2011 and 1 August 2010

Two fascinating sequences of apparently coupled CMEs were observed on 27-28 July 2011 and 1-2 August 2010 by SDO and STEREO. The latter sequence has recently been described at length by Schrijver & Title (2011). In both CME sequences, the individual eruptions were closely synchronized with one another, even though some of them occurred at widely separated locations. In an attempt to identify a plausible reason of such a synchronization, we study the large-scale structure of the background PFSS magnetic fields that were computed from the observed photospheric magnetic field at the appropriate time period. We investigate the magnetic connectivities in these configurations by calculating and analyzing the distributions of the so-called squashing factor at the photospheric and source-surface boundaries, as well as at different cross-sections. This allows us to get a comprehensive understanding of the underlying structural skeleton of the magnetic configuration. In particular, our analysis reveals several pseudo-streamers in the regions where the eruptions occurred. Of special interest to us are the magnetic null points and separators located at the intersection of the separatrix domes and curtains of the pseudo-streamers. We assume that magnetic reconnection induced by the first eruption at these locations played likely a major role in establishing the postulated link between the eruptions in both CME sequences. Our recent simplified MHD model of sympathetic eruptions supports this assumption (Török et al. 2011). In the present study, we try to further verify it by comparing the background magnetic topologies of the two sequences of CMEs. Work supported by NASA and the Center for Integrated Space Weather Modeling (an NSF Science and Technology Center).