The Role of ULF Waves in Ring Current and Radiation Belt Dynamics as Revealed by NASA's Van Allen Probes

NASA's Van Allen Probes have been on orbit since late-August 2012, precessing through all local times over the first two years of the mission, returning high-quality wave and particle observations in the near-Earth space environment. The Probes reveal radiation belt and ring current dynamics with unrivaled accuracy and resolution, providing unambiguous evidence of resonant wave-particle interactions in the inner magnetosphere (e.g., L<7). It is well known that a class of such wave-particle interactions, namely ultra-low frequency (ULF; ~1-10 mHz) wave interactions, contribute to the radial transport of electrons and protons in this region and thus, the large-scale, global morphology of the radiation belts. We focus our investigations on observations of drift-resonance with shock-induced ULF waves, drift-resonance with localized, monochromatic ULF waves, and ULF fluctuations related to nightside particle injections. We also discuss recent advances in the modeling of ULF waves and the challenges that lie ahead.