Poloidal Mode Wave-Particle Interactions Inferred From Van Allen Probes and CARISMA Ground-Based Observations

Abstract

Ultralow-frequency wave and test particle models are used to investigate the pitch angle and energy dependence of ion differential fluxes measured by the Van Allen Probes spacecraft on 6 October 2012. Analysis of the satellite data reveals modulations in differential flux resulting from drift resonance between H+ ions and fundamental mode poloidal Alfvén waves detected near the magnetic equator at L ∼ 5.7. Results obtained from simulations reproduce important features of the observations, including a substantial enhancement of the differential flux between ∼20 and 40° pitch angle for ion energies between ∼90 and 220 keV and an absence of flux modulations at 90°. The numerical results confirm predictions of drift-bounce resonance theory and show good quantitative agreement with observations of modulations in differential flux produced by ultralow-frequency waves.