Interaction of a coronal mass ejection and a stream interaction region: A case study

We investigated the interaction of a coronal mass ejection (CME) and a coronal hole (CH) in its vicinity using remote-sensing and 1 AU in situ data. We used extreme-ultraviolet images and magnetograms to identify coronal structures and coronagraph images to analyze the early CME propagation. The Wind spacecraft and the Advanced Composition Explorer (ACE) provide plasma and magnetic field data of near-Earth interplanetary space. We applied various diagnostic tools to the images and to the time-series data. We find that the CME erupts under a streamer and causes the evacuation of material at its far end, which is observable as dimming and subsequent CH formation. The CME is likely deflected in its early propagation and travels southwest of the Sun-Earth line. In situ data lack signatures of a large magnetic cloud, but show a small flux rope at the trailing edge of the interplanetary CME (ICME), followed by an Alfvenic wave. This wave is identified as exhaust from a Petschek-type reconnection region following the successful application of a Walen test. We infer that the two spacecraft at 1 AU most likely traverse the ICME leg that is in the process of reconnection along the heliospheric current sheet that separates the ICME and the high-speed stream outflowing from the CH.