March 22, 2010, 1:00 pm - 2:00 pm

March 22, 2010, 1:00 pm - 2:00 pm

Current and Future Approaches to Modeling Wave-Particle Interactions in the Radiation Belts

Jay Albert (AFRL)

Physical modeling of Earth’s radiation belts has traditionally been based on radial transport (driven by drift-resonant fluctuations), and pitch angle scattering (driven by interactions with Doppler-shifted gyroresonant waves). In recent years, energization by gyroresonant chorus waves has been also been recognized as a key ingredient. In most large-scale simulations, the gyroresonant interactions are described by bounce-averaged quasilinear theory. A recent 3D, data-driven simulation had good success in modeling the rebuilding of the outer radiation belt during the recovery phase of a moderate storm observed by CRRES, but the main phase dropout was not reproduced very well. Quasilinear theory is appropriate for incoherent interactions with small amplitude, broadband waves, but is highly questionable for coherent interactions with large amplitude, narrowband waves, which constitute chorus. The nonlinear nature of chorus interactions is often studied on a small scale, with large self-consistent codes, but the wave-particle interactions can be loosely described as diffusion, phase bunching, or phase trapping. Notably, phase trapping leads to particle acceleration, but phase bunching is far more common and leads to deceleration and pitch angle decrease towards the loss cone. Analytical expressions have been developed for test particle behavior in each of these regimes, and can be incorporated into diffusion-advection codes similar to current diffusion simulations. Sufficient wave data is just starting to become available to model the nonlinear, advection terms realistically, which may finally lead to good understanding of outer radiation belt dynamics.