Meeting abstract

AGU Fall Meeting, San Francisco, 8-12 December 1997

Abstract: During 1992 and 1993 the Ulysses spacecraft observed a long sequence of Corotating Interaction Regions (CIRs) produced by the interaction of high speed solar wind from the south polar coronal hole with slow speed wind from the near equatorial streamer belt. Stream interfaces in the CIRs separate the plasmas that originated in low speed solar wind and high speed solar wind at their source in the corona, while the heliospheric current sheet (HCS) separates magnetic fields of opposite polarity. A recent paper [Wimmer-Schweingruber et al., J. Geophys. Res., 102, 17407, 1997] has used solar wind composition data to identify the locations of the stream interfaces in a sequence of 16 of the above CIRs. Until March 1993, when Ulysses passed southward of the maximum latitude of the HCS at 30degS, the majority of the CIRs also included a crossing of the HCS, usually located in the region between the forward shock and the stream interface, consistent with the current sheet being embedded in low speed solar wind which has been accelerated by the forward shock of the CIR. In this paper we examine and classify the behaviour of the magnetic field in the vicinity of the HCS crossings and the stream interfaces, and their relative locations, looking for similarities and differences between the signatures over the set of CIRs studied. A variety of HCS crossing signatures are found, some a clean discontinuity between the opposite polarities, others where the crossing is replaced by an apparent flux rope like signature. In some, but not all, cases we find clear magnetic field discontinuities also at the stream interface, although often these don't appear very different from other discontinuities elsewhere in the CIR. The results of this study are of importance in understanding which features within CIRs play a role in the modulation of energetic particle signatures.