Ion composition measurements within magnetospheric flux transfer events

Abstract

Impulsive reconnection near the subsolar magnetopause is a fundamental process of interaction between the magnetosphere and the solar wind flow. Flux Transfer Events (FTEs) appear to be a manifestation of this process. It is therefore important to fully characterize the FTE so as to better understand the physics of the interaction process. We use magnetic field signatures from the AMPTE/CCE spacecraft to identify two magnetospheric FTEs. Electron distributions measured in the plane of the magnetopause inside these FTEs complement previously reported electron measurements. We report, for the first time, ion composition measurements in the energy range ∼0 to 20 keV/e within an FTE. We find that the ion distributions, the ion composition, and the flow velocities are unique to the FTE and unlike either the adjacent magnetosphere, the nearby boundary layer, or the nearby magnetosheath. The H+, He+, and He2+ distribution functions in the FTEs have reversed temperature anisotropies and the relative He2+ abundance is depressed with respect to either the magneosheath or the low latitude boundary layer.