Accelerated electrons in the LLBL as observed by Interball on February 15, 1996

We analyze electron observations in the low latitude boundary layer (LLBL) with the Interball Tail satellite under a southward–duskward magnetosheath magnetic field. It is well known that the LLBL is characterized by bi-directional electron velocity distributions, which leads to an enhancement of the electron temperature. It is also well known that the electron temperature within the LLBL increases with a decrease of the LLBL number density. We found that the parallel electron velocity distribution changes self-consistently with varying number density. Namely, the shape of the parallel velocity distribution does not change in a log–log scale indicating that electron parallel velocities increase proportionately as the number density decreases. This suggests a possible role for the Fermi acceleration mechanism. We also discuss the LLBL topology that is provided by electron velocity distributions.