Plasmaspheric observations at geosynchronous orbit

Yi Jiun Su, Michelle F. Thomsen, Joseph E. Borovsky, Richard C. Elphic, David J. Lawrence, David J. McComas

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7 Scopus citations


The plasmasphere comprises the near-Earth region of the magnetosphere populated by dense, cold plasma of ionospheric origin. The plasmaspheric configuration changes size and shape according to the strength of the convection electric field, which is related to the level of geomagnetic activity. Under quiet conditions, magnetic flux tubes in the outer plasmasphere remain on closed drift paths for days, refilling with ionospheric plasma. We investigate the refilling of flux tubes on their first pass through the dayside region at geosynchronous orbit. The resulting plasmaspheric refilling rate is found to be ~0.25-0.7cm-3h-1, which is comparable with earlier results. Moreover, the refilling rate during periods of increased geomagnetic activity (Kp≥4) is approximately twice the rate obtained at lower levels of geomagnetic activity (Kp≤2). The refilling rate appears to be low in northern winter, however, a strong variation is not found for other three seasons. No strong indication of solar cycle dependence is found from the 3-year data set. When the magnetospheric convection increases, the magnetic flux tubes at the outer plasmasphere find themselves on open drift paths and the cold and dense plasmaspheric material is observed to drain toward the dayside magnetopause. We examine a set of events during times of strong magnetopause compression and erosion in which cold plasmaspheric ions are observed immediately adjacent to magnetosheath ions. The resulting evidence indicates that the draining plasmaspheric ions and entering magnetosheath ions are sometimes simultaneously present on the same flux tube. Moreover, in most of those cases, the detailed velocity-space signatures are consistent with expectations based on the reconnection process. Thus, the dense, cold plasma of the draining plasmasphere participates in the dayside magnetopause reconnection process.

Original languageEnglish (US)
Pages (from-to)1185-1197
Number of pages13
JournalJournal of Atmospheric and Solar-Terrestrial Physics
Issue number11
StatePublished - Jul 2001
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Atmospheric Science
  • Space and Planetary Science


  • Plasma circulation
  • Plasmasphere refilling
  • The fate of plasmaspheric material


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