Using observations from a conjunction of three spacecraft to study the outer radiation belt electron dynamics during the April 20, 2018, geomagnetic storm

In this study, we present results using observations from a conjunction of three satellites to study the outer radiation belt electron dynamics during the April 20, 2018, geomagnetic storm. Between 0900 UT and 1230 UT, Van Allen Probe B, Van Allen Probe A, and Arase were located within similar L-shell ranges (5 – 6) but separated in local time, which provided a unique opportunity to study the variation of electron fluxes along their drift trajectory. The electron fluxes exhibited different responses in three energy ranges: at <∼100 keV, the 90° fluxes remained almost constant while fluxes at lower pitch angles decreased rapidly; for ~100–300 keV, the fluxes decreased at all pitch angles, with larger decreases at larger pitch angles; and at >∼300 keV, the fluxes showed a decrease following the injection closer to local midnight, and an increase further along the drift trajectory toward dawn. To understand the observed flux variations, we calculated the pitch angle and momentum diffusion coefficients and found the results to be consistent with the observations: the pitch angle diffusion coefficients were higher at smaller pitch angles for <~100 keV electrons, and at larger pitch angles for ~100 – 300 keV electrons, while they were low for >~300 keV electrons. The momentum diffusion coefficients were significantly low at all energies. Our results showed that intense chorus waves can drive rapid precipitation of several hundreds of keV electrons on injection timescales (~tens of minutes) and that using multi-spacecraft observations can provide a higher-fidelity picture of the systemic response of the radiation belts to solar wind drivers.