Storm Time Depletions of Multi‐MeV Radiation Belt Electrons Observed at Different Pitch Angles

Abstract During geomagnetic storms, the rapid depletion of the high‐energy (several MeV) outer radiation belt electrons is the result of loss to the interplanetary medium through the magnetopause, outward radial diffusion, and loss to the atmosphere due to wave‐particle interactions. We have performed a statistical study of 110 storms using pitch angle resolved electron flux measurements from the Van Allen Probes mission and found that inside of the radiation belt ( L * = 3 − 5 ) the number of storms that result in depletion of electrons with equatorial pitch angle α eq = 30 ∘ is higher than number of storms that result in depletion of electrons with equatorial pitch angle α eq = 75 ∘ . We conclude that this result is consistent with electron scattering by whistler and electromagnetic ion cyclotron waves. At the outer edge of the radiation belt ( L * ≥ 5.2 ) the number of storms that result in depletion is also large (~40–50%), emphasizing the significance of the magnetopause shadowing effect and outward radial transport.