Pitch-Angle and Energy Electron Fluxes Distributions in the Discrete Aurora

Abstract

The energy and pitch-angle distribution of precipitating auroral electrons determine the efficiency of magnetosphere–ionosphere (MI) coupling. This makes the analysis of their formation important for all types of electron precipitation events, especially for the region of discrete aurora that is associated with the global upward ionospheric current system. We simulate the observed directional and differential energy fluxes in the region of discrete aurora. We found that the observed directional energy flux is more magnetically field-aligned for injected electrons with lower temperature and accelerated in the region located closer to the observer. We conclude that the data of the Science and Technology Satellite-I mission (Park et al., 2014, https://doi.org/10.1002/2013JA019497) with prevailing large pitch angles are dominated by events with high temperatures and/or large distances between the accelerating region and the observer. We also found the observed specific differential energy fluxes of the Fast Auroral Snapshots mission (Dombeck et al., 2018, https://doi.org/10.1029/2018ja025749) can be explained by assuming that every event is composed of particles accelerated by different potential drops. The electron distribution function is calculated from the observed downward and upward energy fluxes. It is constant in some energy range. We found that the plateau boundaries coincide with the region of the positive growth rate of Langmuir-beam waves. This is in agreement with the quasi-linear beam relaxation mechanism proposed to explain the formation of a plateau on the distribution function of precipitating auroral electrons.