Wave-wave and wave-particle interactions in the inner magnetosphere measured with Van Allen Probes: cross coupling between wave modes and its effect on radiation belt dynamics

Abstract:

We will show observations of waveform bursts using the Electric Field and Waves (EFW) burst data on the Van Allen Probes satellites with intermediate frequency waves such as whistler mode, magnetosonic and lower hybrid. These observations show very strong modulation of these waves by lower frequency waves such as EMIC or ULF. We are analyzing the burst data and cross coupling between wave modes to determine how prevalent the cross coupling between wave modes is and under what conditions it occurs. To supplement the EFW data, each satellite is also equipped with a full complement of particle instruments, including the HOPE instrument measuring lower energy (1 eV – 50 keV) particles and MagEIS instruments measuring higher energy (20 keV – 5 MeV) particles. The energy and angular resolution of these detectors are sufficient to resolve the scattering and energization arising from the distinct wave modes, using the signatures in the trapped electron populations predicted by theory for the various mechanisms. Comparison of the burst waveform data with the electron data from HOPE and MagEIS, for times with and without coupling between the wave modes, will allow us to identify how the cross coupling affects electron dynamics in the radiation belts.

The significance of wave-particle interactions in the formation and depletion of the radiation belts has long been established, but is still not completely understood. Specifically, pitch angle scattering from waves such as plasmaspheric hiss and electromagnetic ion cyclotron [EMIC] waves near the duskside plasmapause is known to contribute to electron loss from the radiation belts, primarily through precipitation into the atmosphere. Higher frequency waves such as whistler mode chorus and magnetosonic waves observed near the equator in the lower hybrid frequency range are widely believed to be primary means for electron energization. However, these and other competing processes often occur simultaneously, and an accurate model of radiation belt dynamics must account for the relative influence of all these processes over time. Additionally, analysis of the coupling between wave modes over the course of auroral storms and substorms, periods of extremely complex interaction and energy transfer, could increase our understanding of storm time radiation belt dynamics.