Combined Ulysses solar wind and SOHO coronal observations of several west limb coronal mass ejections

Abstract

From October 1996 to January 1997, Ulysses was situated roughly above the west limb of the Sun as observed from Earth at a heliocentric distance of about 4.6 AU and a latitude of about 25°. This presents the first opportunity to compare Solar and Heliospheric Observatory (SOHO) limb observations of coronal mass ejections (CMEs) directly with their solar wind counterparts far from the Sun using the Ulysses data. During this interval, large eruptive events were observed above the west limb of the Sun by the Large Angle Spectrometric Coronagraph (LASCO) on SOHO on October 5, November 28, and December 21–25, 1996. Using the combined plasma and magnetic field data from Ulysses, the October 5 event was clearly identified by several distinguishing signatures as a CME. The November 28 event was also identified as a CME that trailed fast ambient solar wind, although it was identified only by an extended interval of counterstreaming suprathermal electrons. The December 21 event was apparently characterized by a 6‐day interval of nearly radial field and a plasma rarefaction. For the numerous eruptive events observed by the LASCO coronagraph during December 23–25, Ulysses showed no distinct, individual CMEs, perhaps because of intermingling of two or more of the eruptive events. By mapping the Ulysses observations back in time to the Sun assuming a constant flow speed, we have identified intervals of plasma that were accelerated or decelerated between the LASCO and Ulysses observations.