A CME-DRIVEN SOLAR-WIND DISTURBANCE OBSERVED AT BOTH LOW AND HIGH HELIOGRAPHIC LATITUDES

A solar wind disturbance produced by a fast coronal mass ejection, CME , that departed from the Sun on Feburary 20, 1994 was observed in the ecliptic plane at 1 AU by IMP 8 and at high heliographic latitudes at 3.53 AU by Ulysses. In the ecliptic the disturbance included a strong forward shock but no reverse shock, while at high latitudes the distur bance was bounded by a relatively weak forward-reverse shock pair. It is clear that the disturbance in the ecliptic plane was driven primari ly by the relative speed between the CME and a slower ambient solar wi nd ahead, whereas at higher latitudes the disturbance was driven by ex pansion of the CME. The combined IMP 8 and Ulysses observations thus p rovide a graphic illustration of how a single fast CME can produce ver y different types of solar wind disturbances at low and high heliograp hic latitudes. Simple numerical simulations help explain observed diff erences at the two spacecraft.