Ionospheric ions in the near-Earth magnetotail

Abstract

[1] We report studies of the relationship between geomagnetic storms and the spatial distribution of cold ions, mostly of ionospheric origin, in the near-Earth magnetotail using in situ particle and field measurements from the Polar spacecraft, solar wind measurements from the ACE spacecraft, and ground geomagnetic indices, during the years from 2000 to 2005. We find local time and latitude-dependent distributions of the plasma moments of cold ions at various levels of geomagnetic storms characterized by the Sym-H and Dst indices. (1) Denser cold ions were observed at the duskside (N > 10 cm−3 compared with 1 cm−3 on average): consistent with the formation of plasma plumes and enhanced bulge region formed as the cold ions wrapped under corotation. (2) Higher temperatures were observed in the auroral oval regions, and a larger temperature anisotropy was observed at the dawnside. (3) Heating processes were strongest near midnight and in the auroral oval regions, which map to PSBL or CPS, except during extremely high geomagnetic activity levels, when heating occurred at high latitudes toward the dawnside, which map to the plasma mantle or distant magnetotail. We interpret these variations as results of ionospheric outflows and plasmaspheric expansion interacting with enhancements of near-Earth magnetospheric convection and geomagnetic-storm-related heating processes in the magnetotail.