Drift echoes and flux oscillations: A signature of prompt and diffusive changes in the radiation belts

Abstract

Prompt creation of new multi-MeV electron and proton radiation belts in the normally benign slot region between inner and outer Van Allen zones was observed by the short-lived Combined Release and Radiation Effects Satellite (CRRES) mission almost 30 years ago. Flux oscillations at lower energies coincident with ULF wave measurements and consistent with drift resonance were also a feature of the CRRES observations. The next mission designed to study the radiation belts in similar detail from a near equatorial plane orbit was the Van Allen Probes launched in August 2012. These twin spacecraft in similar orbits observed many milder events which produce drift echoes indicative of injection over a limited range of longitude on less than an electron drift time. Related substorm injection drift echoes were also observed by Van Allen Probes with much higher energy resolution than previously. Along with other flux oscillations associated with Ultra Low Frequency (ULF) waves, these events form a class which contributes to the overall radial transport and energization of radiation belt electrons as well as protons. This paper focuses on the greatly improved measurements from the Van Allen Probes relative to the CRRES era. These measurements illuminate our understanding of the importance of flux oscillations as a signature of radial transport relative to other energization and loss processes affecting the radiation belts.