Nonlinear Whistler Wave Physics in the Laboratory and in the Radiation Belts

Recent experiments at NRL on the interaction of electron beams with whistler waves revealed interesting new wave dynamics such as (1) large sub-packet amplitude modulations, (2) discrete changes in frequency between sub-packets, (3) multiple chirping waves at nearby frequencies, and (4) parametric decay of chirping whistlers. These experiments inspired a reanalysis of high time resolution waveform data from the Van Allen Probes of whistler mode chorus in the Earth’s outer radiation belts. We developed a Bayesian spectral analysis technique that uses non-stationary time-domain models for the waves which revealed many features of chorus that are seen in laboratory data. These laboratory and space observations inspired a new finite-dimensional self-consistent Hamiltonian model in which solutions that exhibit sub-packet structuring were found. These solutions exhibit not a single island forming in phase space but a pair of islands. The self-consistent rotation in phase space of the two islands leads to the dramatic amplitude modulations that form sub-packets. These models are tractable enough to incorporate into waveform models of observed time-series to further the development of a self-consistent theory of nonlinear wave-particle interactions.