Plasmaspheric material at the reconnecting magnetopause

Abstract

During geomagnetic storms, cold and dense plasmaspheric material is observed to drain toward the dayside magnetopause when the solar wind pressure is strong and the interplanetary magnetic field (IMF) is southward. What is the fate of draining plasmaspheric material at the magnetopause? Does the plasmaspheric material participate in the dayside reconnection and then convect on open field lines through the polar cap? Or does the material become captured into the low-latitude boundary layer and then convect on closed field lines around the flanks of the magnetosphere? In this paper, we present observations from the Los Alamos magnetospheric plasma analyzers (MPA) onboard five satellites at geosynchronous orbit during 86 plasmaspheric drainage events. For a set of events where cold plasmaspheric material is observed immediately adjacent to the magnetopause/low-latitude boundary layer, we examine the detailed ion distributions, from ∼1 eV to ∼40 keV, for evidence that the draining plasmaspheric ions and the entering magnetosheath ions are simultaneously present on the same flux tube. Ten cases out of 57 are found where magnetosheath ions and plasmaspheric ions were unambiguously present simultaneously in the same flux tube, which is a signature that the plasmaspheric flux tubes do experience dayside reconnection. An additional ten cases strongly, but not as definitively, support this conclusion. Further, six of seven events with available IMF information have velocity space signatures that are consistent with expectations based on the reconnection process. Copyright 2000 by the American Geophysical Union.