Open AccessIon composition of the near‐Earth plasma sheet in storm and quiet intervals: Geotail/EPIC measurements
Author(s) -
Nosé M.,
Ohtani S.,
Takahashi K.,
Lui A. T. Y.,
McEntire R. W.,
Williams D. J.,
Christon S. P.,
Yumoto K.
Publication year - 2001
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2000ja000376
Subject(s) - plasma sheet , geomagnetic storm , physics , ion , plasma , geophysics , atmospheric sciences , storm , flux (metallurgy) , atomic physics , quiet , astrophysics , solar wind , magnetosphere , materials science , meteorology , astronomy , nuclear physics , quantum mechanics , metallurgy
We investigate the ion composition of the near‐Earth plasma sheet in storm and quiet intervals, using energetic (9–210 keV) particle flux data obtained by the suprathermal ion composition spectrometer (STICS) sensor of the energetic particle and ion composition (EPIC) instrument on the Geotail spacecraft. In 1998 four magnetic storms (minimum Dst <−50 nT) occurred when Geotail was located in the near‐Earth plasma sheet ( X ≥−10 R E ). For each of the storms, we have selected a corresponding quiet interval from time periods when Geotail revisited the near‐Earth plasma sheet under the condition Dst >−20 nT. The energy density of the H + , He + , and O + ions was computed from the EPIC/STICS data for these storm and quiet‐time events. We obtained the following results: (1) The energy density is higher during storms than during quiet times for all ion species (H + , He + , and O + ); (2) the He + /H + energy density ratio during storms is 0.01–0.02, while that during quiet times is ∼0.01; and (3) the O + /H + energy density ratio is significantly larger during storms (0.2–0.6) than during quiet times (0.05–0.1). To explain these results we suggested a current sheet acceleration mechanism in which ions are energized by the dawn‐to‐dusk convection electric field in a mass‐dependent way in the course of interaction with the current sheet.