Speaker
Description
Very Low Frequency (VLF) whistler-mode chorus and hiss emissions are pervasive features of the Earth’s magnetosphere, playing a critical role in controlling the dynamics of the outer Van Allen radiation belt. Through interactions with trapped electrons, these waves drive both upper-atmosphere ionization and the energization of relativistic electrons, posing significant space weather hazards to satellite infrastructure and astronauts. While current wave models generally correlate wave amplitude enhancements with rising geomagnetic activity, this approach is insufficient to explain the fine-scale dynamics observed during storm events. Notably, historical analyses reveal that geomagnetic storms produce highly variable outcomes, with geosynchronous fluxes increasing in only 53% of events, while decreasing or remaining unchanged in others. This variability suggests the presence of critical, unaccounted factors that govern the global efficiency of wave-particle interactions and determine the predominance of scattering versus acceleration regimes. Key factors recently identified to affect this efficiency include: (i) the dependence of chorus frequency on latitude, which lowers the electron scattering resonance; (ii) the latitudinal distribution of wave amplitude and high-latitude wave extent; (iii) the distribution of wave normal angles, specifically the influence of oblique whistler populations; and (iv) background plasma characteristics, particularly the coupling of cold plasma density with hot electron populations. In this study, show the importance of the integrated approach (which includes a comprehensive combination of the local parameters) to estimations of wave-particle interactions efficiency in the radiation belts and present a survey of MeV electron pitch angle and energy quasi-linear diffusion rates driven by chorus and hiss waves as a function of L-shell, local time, and AE index. Our model accounts for the local electron plasma frequency to gyrofrequency ratio (fpe/fce), chorus wave frequency, and resonant wave amplitude. We demonstrate that during disturbed periods, the fpe/fce ratio strongly decreases in the night sector. This leads to faster electron loss, but also significantly faster electron energization in two distinct regions: just above the plasmapause and at L = 3.5– 5.5. We conclude that spatiotemporal variations of fpe/fce with the AE index shape the evolution of electron energization in the outer belt, leading to extremely short time scales for quasi-linear MeV electron acceleration, in agreement with Van Allen Probes observations during the intense geomagnetic storms.