Multi-Spacecraft Observations of an Interplanetary Coronal Mass Ejection Interacting with Two Solar Wind Regimes Observed by the Ulysses and Twin-STEREO Spacecraft

Abstract

We present a combined study of a coronal mass ejection (CME) revealed in a unique orbital configuration which permits the analysis of remote-sensing observations on 27 June 2007 from the twin Solar Terrestrial Relations Observatory (STEREO) -A and -B spacecraft and of its subsequent in situ counterpart outside the ecliptic plane, the interplanetary coronal mass ejection (ICME) observed on 04 July 2007 by Ulysses at 1.5AU and Heliographic Earth Ecliptic coordinate system (HEE) 33° latitude and 49° longitude. We apply a triangulation method to the STEREO Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) COR2 coronagraph images of the CME, and a self-similar expansion fitting method to STEREO/SECCHI Heliospheric Imager (HI)-B. At Ulysses we observe: a preceding forward shock, followed by a sheath region, a magnetic cloud, a rear forward-shock, followed by a compression region due to a succeeding high-speed stream (HSS) interacting with the ICME. From a minimum variance analysis (MVA) and a length-scale analysis we infer that the magnetic cloud at Ulysses, with a duration of 24h, has a west-north-east configuration, length scale of ≈0.2AU, and mean expansion speed of 14.2 kms−1. The relatively small size of this ICME is likely to be a result of its interaction with the succeeding HSS. This ICME differs from the previously known over-expanding types observed by Ulysses, in that it straddles a region between the slow and fast solar wind that in itself drives the rear shock. We describe the agreements and limitations of these observations in comparison with 3D magneto-hydrodynamic (MHD) heliospheric simulations of the ICME in the context of a complex solar wind environment.