Radiation Belt “Dropouts” and Drift-Bounce Resonances in Broadband Electromagnetic Waves

Observations during the main phase of geomagnetic storms reveal an anticorrelation between the occurrence of broadband low-frequency electromagnetic waves and outer radiation belt electron flux. We show that the drift-bounce motion of electrons in the magnetic field of these waves leads to rapid electron transport. For observed spectral energy densities it is demonstrated that the wave magnetic field can drive radial diffusion via drift-bounce resonance on time scales less than a drift orbit. This process may provide outward transport sufficient to account for electron “dropouts” during storm main phase and more generally modulate the outer radiation belt during geomagnetic storms. Kinetic eigenmodes of the geomagnetic field may deplete the outer radiation belt during the main phase of geomagnetic stormsDrift-bounce resonances with the wave magnetic field can drive radial diffusion on time scales less than a drift periodBroadband electromagnetic waves commonly observed in the inner magnetosphere during geomagnetic storms may be an important unrecognized driver of radiation belt dynamics