Charged particle behavior in localized ultralow frequency waves: Theory and observations

The formation and variability of the Van Allen radiation belts are highly influenced by charged particles accelerated via drift‐resonant interactions with ultralow frequency (ULF) waves. In the prevailing theory of drift resonance, the ULF wave amplitude is assumed independent of magnetic longitude. This assumption is not generally valid in Earth's magnetosphere, as supported by numerous observations that point to the localized nature of ULF waves. Here we introduce a longitude dependence of the ULF wave amplitude, achieved via a von Mises function, into the theoretical framework of ULF wave‐particle drift resonance. To validate the revised theory, the predicted particle signatures are compared with observational data through a best fit procedure. It is demonstrated that incorporation of nonlocal effects in drift‐resonance theory provides an improved understanding of charged particle behavior in the inner magnetosphere through the intermediary of ULF waves. The prevailing theory of ULF wave‐particle drift resonance is extended by considering the local time dependence of the ULF wave amplitude Incorporation of nonlocal effects in drift‐resonant process provides improved understanding of particle behavior in the inner magnetosphere The newly predicted signatures are consistent with observations from IGSO spacecraft, which validates the revised drift‐resonance theory