Meeting abstract

AGU Fall Meeting, San Francisco, 15-19 December 1996

Abstract:
Ulysses' unique trajectory has enabled, for the first time, direct, accurate and uninterrupted observation of a large number of Interplanetary Coronal Mass Ejections (ICMEs) at a wide range of heliolatitudes. We have examined the magnetic signatures of 57 ICMEs and compared their start and stop times to the start and stop times as derived from the solar wind observations (González-Esparza et al., 1996). We find that some magnetic signatures which are clearly associated with the ICMEs precede the plasma ICME start time and some extend beyond the plasma stop time. We have used both low variance and a smooth field rotation as characterising the magnetic fields assocaited with ICMEs. The statistics of the relationship between the durations in the magnetic field and plasma signatures are presented. The internal magnetic structure of an ICME is highlighted for one particular event - two ICMEs occurring on July 16th, 1992 and July 24th, 1992. The ICMEs, between them, are believed to have temporarily deflected the heliospheric current sheet equatorward of its expected position (Balogh et al., 1993). A Minimum Variance Analysis of the magnetic field in the first CME of the two reveals two distinct magnetic regimes - a proposed cylindrical topology followed by a region of constant, almost unidirectional magnetic field lines.