On the connection between large-amplitude whistlers, microbursts and nonlinear kinetic structures in the Earth's Radiation Belt

Abstract:

Using a dynamical-system approach we have investigated the efficiency of large-amplitude whistler waves for causing microburst precipitation in planetary radiation belts by modeling the microburst energy and particle fluxes produced as a result of non-linear wave-particle interactions. We show that wave parameters consistent with large-amplitude oblique whistlers commonly generate microbursts of electrons with hundreds of keV-energies, as a result of Landau trapping. Relativistic microbursts (> 1 MeV) can also be generated by a similar mechanism, but require waves with large propagation angles θ_kB > 50^o and phase-speeds v_Φ > c/9. Using our result for precipitating density and energy fluxes, we argue that holes in the distribution function of electrons near the magnetic mirror point can result in the generation of electrostatic structures consistent in scales (of the order the Debye length) and electric field amplitudes (of the order of 1 mV/m) to nonlinear structures observed in the radiation belts by the Van Allen Probes. Our results indicate a relationship between nonlinear electrostatic and electromagnetic structures in the dynamics of planetary radiation belts and their role in the cyclical production of energetic electrons (i.e. E > 100 keV) on kinetic timescales, that is much faster than previously inferred.