Large-Amplitude whistler waves and electron acceleration in the earth's radiation belts: A review of STEREO and wind observations

One of the critical problems for understanding the dynamics of Earth's radiation belts is determining the physical processes that energize and scatter relativistic electrons. We review measurements from the Wind/Waves and STEREO S/Waves waveform capture instruments of large-amplitude whistler mode waves. These observations have provided strong evidence that large amplitude (100s of mV m-1) whistler mode waves are common during magnetically active periods. The largeamplitude whistler mode waves are usually nondispersive and obliquely propagating, with a large longitudinal electric field and significant parallel electric field. These characteristics are different than those of typical chorus, though it remains to be seen whether the large-amplitude whistler mode waves are a subpopulation of chorus or something else entirely. We will also review comparisons of STEREO and Wind wave observations with SAMPEX observations of electron microbursts. Simulations show that the waves can result in electron energization by many MeV and/or scattering by large pitch angles during a single wave packet encounter due to coherent, nonlinear processes including trapping. The experimental observations combined with simulations suggest that quasilinear theoretical models of electron energization and scattering via small-amplitude waves, with timescales of hours to days, may be inadequate for understanding radiation belt dynamics.