Analysis of the Evolution and Interaction of Multiple Coronal Mass Ejections and Their Shocks in July 2012

After a long-lasting solar minimum (2007-2009), the Sun has been getting more active since 2010. Many coronal mass ejections have erupted and interacted with each other and with the non-uniform solar wind medium since August 2010. Many sizable CMEs erupted in July 2012 alone. Three consecutive CMEs were observed on July 17 (~13:54UT), July 18 (~06:24UT), and July 19 (~05:39UT) from different source regions located at S23W61, N18W180, and S17W92, with speeds of 802, 713, and 1160 km/s, respectively. Multiple interplanetary (IP) shocks and CMEs arrived at the twin STEREO-A/B spacecraft, at ACE and at WIND after these CMEs erupted from the Sun. (STEREO-A and -B were orbiting near 121 degrees west and 114 degrees east of Sun-Earth-line. The orbit of ACE was at L1 and Wind was near the Sun-Earth line.) In order to understand the causes of these multiple IP shocks/CMEs, we employ a global three-dimensional simulation model, H3DMHD (HAF+3DMHD, Wu et al., 2007, JGR) to study the evolution of these IP shocks/CMEs, and the interaction between them. The simulation results are presented as follows. (1) A shock (or the flank of a shock) arrived at each of these spacecraft on the same day (July 20). (2) These shocks/ICMEs are generated from different source regions. An IP shock driven by the July 18 CME arrived at STEREO-B first, another IP shock driven by the July 19 CME arrived at STEREO-A, and then the flank of a shock driven by the July 17 CME arrived at Earth. The detailed observations (from both coronal images and in-situ solar wind data), simulated results and comparison between simulations and observations will be presented.