M S Gussenhoven
F Rich; D A Hardy; C Y Huang;
Three distinct populations in the magnetosphere are believed to result from near-direct entry of solar wind particles: 1) the cusp population near noon; 2) the boundary populations at high latitudes on the flanks of the magnetosphere; and 3) the polar rain. The position and extent of these populations have been shown to vary strongly with Bz and, in some cases, with solar wind speed, IMF sector, magnetic activity and season. Direct comparison of the three populations with each other and with the assumed parent population are rare, and somewhat troubling in their differences. A variety of uncoordinated efforts have been made to explain away the differences, yet no clear picture of the relationships between the four populations has emerged. During the more than 24 hour period on October 19-20, 1995, in which a magnetic cloud passed by the magnetosphere, the solar wind speed, magnetic field magnitude and IMF sector were near constant, while Bz, the ion density and the ion temperature underwent major changes, for the most part, in a steady manner. Ignoring the morphological changes in cusp, boundary and polar rain populations due to changes in Bz, we compare changes in densities and temperatures to those in the solar wind and relate these to possible entry scenarios.
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