Effect of the mirror force on the collision rate due to energetic electron precipitation: Monte Carlo simulations

Abstract

We study the effect of the mirror force on the collision rate due to the energetic electron precipitation into the ionosphere. We develop a simulation code for the motion of energetic electrons with the mirror force to solve the variation of the pitch angle of electrons during their precipitation. In this code, a module computing the collision between precipitating energetic electrons and neutral gas using the Monte Carlo method is employed. By combining the developed modules, altitude profiles of the collision rate due to energetic electron precipitation in the keV energy range are investigated, and the effect of the mirror force acting on precipitating electrons is examined. The simulation results show that the influence of the mirror force on the altitude profile of the collision rate is significant for electrons with a high initial pitch angle, corresponding to the pitch angle close to the loss cone. The effect of the mirror force results in the broadening of the altitude profile of the collision upward due to the reflection of mirroring electrons. Simulation results for energetic electrons with kinetic energies above 100 keV show that a secondary peak near the mirror point is formed in the altitude profile of the collision rate. The formation of the secondary peak can be explained by the stagnation of electrons around the mirror point. The relatively long duration staying in neutral gas results in the increase of the collision rate around the mirror point, against the smaller collision cross-section in the higher energy range. Simulation results reveal that the maximum collision rate in the altitude range lower than 100 km becomes one order of magnitude smaller if electrons in the kinetic energy range larger than tens of keV precipitate with the pitch angle close to the loss cone. The results of the present study emphasize the importance of the mirror force for the precise modeling of ionospheric response due to the energetic electron precipitation.

Improved Energy Resolution Measurements of Electron Precipitation Observed During an IPDP‐Type EMIC Event

“…Quantifying and characterizing energetic electron precipitation (EEP, i.e., >10 keV) is one of the requirements for a more complete description of solar forcing that can be used in coupled climate models (Duderstadt et al., 2021; Matthes et al., 2017; Nesse Tyssøy et al., 2021; Salice et al., 2024; Seppälä et al., 2015; van de Kamp et al., 2016). Electrons precipitating with energies >10 keV will typically deposit their energy in the atmosphere at altitudes of 100 km or below (Katoh et al., 2023; Turunen et al., 2009; Xu et al., 2020), leading to chemical and dynamical changes in the climate system (Andersson et al., 2012; Brasseur & Solomon, 2005; Guttu et al., 2021; Mironova et al., 2015; Orsolini et al., 2018; Sinnhuber et al., 2012). One mechanism that causes energetic electron precipitation is via scattering with EMIC waves (e.g., Denton et al., 2019; Millan & Thorne, 2007; Thorne & Kennel, 1971).…”