Energetic Electron Flux Dropouts Measured by ELFIN in the Ionospheric Projection of the Plasma Sheet

Abstract

Low‐altitude observations of magnetospheric particles provide a unique opportunity for remote probing of the magnetospheric and plasma states during active times. We present the first statistical analysis of a specific pattern in such observations, energetic electron flux dropouts in the low‐altitude projection of the plasma sheet. Using 3.5 years of data from the ELFIN CubeSats we report the occurrence distribution of 145 energetic electron flux dropout events and identify characteristics, including their prevalence in the dusk and premidnight sectors, their association with substorms and enhanced auroral activities, and their correlation with the region‐1 (R1) field‐aligned current region. We also investigate three representative dropout events which benefit from satellite conjunctions between ELFIN, GOES, and THEMIS, to better understand the magnetospheric drivers and magnetic field conditions that lead to such dropouts as viewed by ELFIN. One class of dropouts may be associated with magnetic field mapping distortions due to local enhancements and thinning of cross‐tail current sheets and amplification of R1 field‐aligned currents. The other class may be associated with the increase in perpendicular anisotropy of magnetospheric electrons due to magnetic field dipolarizations near premidnight. These plasma sheet flux dropouts at ELFIN provide a valuable tool for refining magnetospheric models, thereby improving the accuracy of field‐line mapping during substorms.

Dispersed Relativistic Electron Precipitation Patterns Between the Ion and Electron Isotropy Boundaries

“…We attribute both deviations from expected behavior to dipolarizations and associated injections, like the transient dipolarizations seen at THEMIS D at ∼11:35 UT and ∼11:59 UT (see Y. Shen et al, 2023, for detailed analysis of such type of transient events). In such instances, the mapping changes abruptly (with the sudden appearance of dipolarized flux bundles in the inner magnetosphere and at the near-Earth plasma sheet) causing a fixed latitude in the ionosphere previously projected to the mid-tail plasma sheet to rapidly map to lower L-shells, well within the inner magnetosphere (Chu et al, 2015;Nikolaev et al, 2015).…”