Wave-Particle Interactions in Earth's Radiation Belts: A Model Study of Correlated Electron Bursts and Whistler Chorus

The Van Allen Probes commonly observe events of quasiperiodic energetic electron bursts correlating with simultaneously detected upper-band, whistler-mode chorus emissions during the recovery of substorm plasma injections. These electron bursts exhibit narrow ranges of pitch angles (75-80° and 100-105°) with energies of 20-40 keV. Electron cyclotron harmonic (ECH) emissions are also commonly detected, but typically do not display correlation with the electron bursts. Using the observed electron velocity distribution from an event on January 13, 2013 as starting parameters for a particle in cell (PIC) simulation, the effects of temperature anisotropy (perpendicular temperature greater than parallel temperature), presence of a loss cone, and a cold electron population on the generation of whistler and ECH waves are examined to understand wave generation and nonlinear interactions with the particle population. These nonlinear interactions produce energy diffusion and strong pitch angle scattering into the loss cone on the order of milliseconds, which is faster than a typical bounce period of seconds. The quasiperiodic nature of the electron bursts is examined by implementing a loss-cone and/or temperature anisotropy recycling technique to model the effects of the periodic emptying of the loss cone and anisotropic electron injections on the growth of the whistler and ECH waves. Recycling the temperature anisotropy results in a new burst of whistler mode waves suggesting that an individual electron injection is sufficient to excite new waves if it raises the anisotropy of the electron velocity distribution beyond the whistler instability threshold. Recently, an inhomogeneous curved magnetic field has been implemented in the simulation to study the excitation of whistler chorus elements and determine the nonlinear effects on the particle population. The simulation results are compared to the Van Allen Probe observations to determine electron acceleration, heating, and transport in Earth's radiation belts due to wave-particle interactions.