The Deflection of CMEs During Instances of CME-CME Interactions

The interaction of successive coronal mass ejections (CMEs) can be directly imaged by remote-sensing instruments such as the HIs onboard STEREO and the resulting transients can be measured in situ by spacecraft such as STEREO-A, STEREO-B, ACE and Wind. Here, we present the analysis of two successive CMEs from May 2010, observed to interact within HI1 field-of-view. During the interaction, the second CME (CME2) is found to decelerate and the first CME (CME1) is found to get compressed. At 1 AU, Wind observed a single, typical magnetic cloud-like ejecta. By combining the different observations, we determine that this event shows a clear instance of the deflection of two CMEs due to their collision in the heliosphere, and we estimate the deflection of CME1 to be about 10 degrees in the longitudinal direction. The resulting ejecta at 1 AU has a duration in agreement with the previously proposed hypothesis that compressed CMEs may over-expand after the end of the interaction. We also discuss additional events of CME-CME interaction and relate the findings to previous simulation efforts.