LLBL Contribution to the Plasma Sheet Ions

Abstract

The cold dense ions along the plasma sheet flanks have been previously observed during periods of northward interplanetary magnetic field (IMF) with in situ satellites and have been interpreted in terms of low latitude boundary layer (LLBL) ion entry into the plasma sheet. We have previously developed a method for inferring plasma sheet ion temperature (T), density (n), and pressure (p) from ionospheric observations. Using this method and DMSP observations for 1992, we present 2D profiles of the equatorial plasma sheet ion n and T for southward and northward IMF for quiet and moderate magnetic activity. The results show the spatial extent of the cold dense ions in more detail than previously shown. The plasma sheet ion n and T profiles generally differ between the northward and southward IMF cases, but they exhibit the sharpest contrast along the flanks. During periods of northward IMF, cold dense ions can be found plentifully along the plasma sheet flanks. However, during periods of southward IMF, the presence of these cold dense ions is noticeably diminished, especially alongthe dusk flank where the density peak is barely discernible. The result here suggests that any mechanism proposed to transport magnetosheath ions from dusk LLBL to the plasma sheet during periods of northward IMF has to be able to do it on a massive scale efficiently. A recent Geotail case study along with a magnetohydrodynamic (MHD) simulation of the same event suggest that the Kelvin-Helmholtz instability can be one such mechanism.