High-Resolution Study of the Relationship Between the Region 2 Birkeland Current Equatorward Boundary and Soft Electron Fluxes

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The nightside Region 2 (R2) Field Aligned Current (FAC) system is associated with magnetospheric dynamics occurring close to the inner magnetosphere. The current carriers for this system have been studied extensively at higher energies. In this study, we investigate the potential role of electrons in the less studied suprathermal (sub-keV) range. The Enhanced Polar Outflow Probe (e-POP) instrument suite on the CASSIOPE satellite (Swarm Echo) consists of eight plasma instruments, including the Suprathermal Electron Imager (SEI) and the magnetic field instrument (MGF). The SEI records two-dimensional energy-angle images of electron distribution for energies up to 350 eV at a rate of 100 images per second. The MGF samples the magnetic field at a sampling rate of 160 times per second with a resolution of 0.0625 nT. Even though ePOP, whose scientific focus is polar outflow, does not detect high-energy particles ($>$ 1 keV), its polar orbit is optimal for studying current carriers of FACs. We examine suprathermal electron fluxes over the region of 45-80º magnetic latitude during different geomagnetic conditions based on 25 traversals of the R2 boundary. These range from 1700-0400 MLT during which the SEI detects enhanced suprathermal electron fluxes in the 5-100 eV energy range just equatorward of the R2 boundary. Coincident with these fluxes and in a majority of cases, we see evidence of a current in the opposite direction of the R2 current, which we believe has not been reported previously.
Birkeland currents, Field aligned currents, Cassiope ePOP, Swarm, POES, Suprathermal electrons, SEI
Liyanage, G. (2023). High-resolution study of the relationship between the Region 2 Birkeland current equatorward boundary and soft electron fluxes (Unpublished master's thesis). University of Calgary, Calgary, AB.