Systematic detection and analysis of low-intensity particle environments within Earth's magnetotail for the presence of anisotropy and plasma bulkflow

A statistical survey has been done on four large time-continuous intervals of ∼0.05 to ∼0.5 MeV proton, helium, and oxygen observations taken by the GEOTAIL/EPIC ICS instrument in the near, mid, and deep magnetotail. A magnetosheath interval was included to show contranst with magnetotail results. The purpose of the analysis was to infer the particle and plasma characteristics that produced the particle distributions seen by the EPIC ICS instrument and to characterize the typical magnetotail plasma, field, and energetic particle conditions. Many earlier studies have considered unusually intense fluxes and disturbed conditions. Here we take the magnetotail in “as is” condition. The analysis produced flow direction distributions that are asymmetric in the neartail region, which contains dawn to dusk, tailward and sunward flows. The flow direction in the midtail region and farther downstream is strongly tailward. The modal bulkflow velocity is increased between the neartail and midtail regions. The proton and oxygen particle populations become the dominant species in the deeptail region. The oxygen particle contribution to the magnetosphere's energy budget is significantly increased in the deeptail region.