Diagnosing the Rapid Loss of Outer Radiation Belt Electrons Due To Strong Chorus‐Driven Wave‐Particle Interactions Along an Electron Injection Path

Multi‐spacecraft data demonstrate that intense chorus waves are excited during electron injection events that drive rapid radiation belt electron loss across a limited energy range from ∼100 to 300 keV on sub‐drift timescales through strong pitch angle diffusion. We use a conjunction of Van Allen Probe A, B, and Arase spacecraft to study the variation of electron fluxes along an electron injection path in the energy range of∼30 keV–1 MeV during the 20 April 2018, geomagnetic storm. At <∼100 keV, the 90° fluxes remained almost constant; for ∼100–300 keV, the fluxes decreased at all pitch angles; and at >∼300 keV, the fluxes showed ade crease following the injection closer to local midnight, and an increase further along the drift trajectory toward dawn. We calculate electron pitch angle and momentum diffusion coefficients in the observed waves using aquasi‐linear approximation: fast losses only occurred at lower pitch angles at <∼100 keV but reached the core distribution for ∼100–300 keV. For >∼300 keV, the overall pitch angle diffusion is weak, but energy diffusion acts to increase the electron flux along the injection path. The results indicate that intense chorus waves drive loss on timescales of ∼10s of minutes through strong pitch angle diffusion that is localized in energy and local time, consistent with the observations. Overall, electron injection events should be associated with intense losses in a limited energy range, the resulting atmospheric impacts having strong local‐time dependence, with preferential energy deposition in the morning sector during substorm injections.