Cassini Plasma Spectrometer electron spectrometer measurements during the Earth swing-by on August 18, 1999

On August 18, 1999, Cassini flew by the Earth on its way to Saturn. The Cassini Earth swing-by was the fastest traversal of the Earth's magnetosphere to date. The spacecraft was traveling at 9.1 R-E hr(-1) (16.1 km s(-1)) and made rapid traversals of several regions of the terrestrial magnetosphere. During the Cassini Earth swing-by the Electron Spectrometer (ELS) collected almost 9 hours of data in the Earth's magnetosphere and almost 10 hours of solar wind data upstream of the Earth. During the pass, Cassini ELS sampled electrons in the solar wind, bow shock, magnetosheath, magnetopause, radiation belts, plasmasphere, plasma sheet, lobes, and crossings of the tail magnetopause. The purpose of this paper is (1) to give a summary of electron observations including the locations of magnetosphere boundary crossings and (2) to assess how the ELS is functioning as it takes measurements in the greatly differing plasma regimes encountered. Results are shown to be mainly consistent with previous observations with a few exceptions. In addition to anticipated results we present evidence of a low-energy field-aligned beam in the plasma sheet and evidence of asymmetry on the dayside and nightside plasmapause position. Preliminary calculations of density and temperature for the solar wind, magnetosheath, and plasma sheet are also presented.

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