Dependence of the quasi-linear scattering rates on the wave normal distribution of chorus waves

Abstract

The sensitivity of quasi-linear scatterin rates to the wave normal distribution of chorus waves is studied using the Full Diffusion Code newly developed at the University of California, Los Angeles. Scattering rates are computed for field-aligned, oblique (∼20° wave normal angles), and highly oblique (∼40° wave normal angles) cases. For radiation belt electrons, scattering rates are relatively insensitive to the assumed distribution of wave normal angles at high energies; while when the energy is smaller, in the range of tens of keV, knowledge of the wave normal distribution becomes important. It is shown that Landau resonance becomes very important for the scattering of electrons with energies of tens of keV as waves become more oblique. Scattering rates for various order resonances and energies are presented. Our results show that, for a fixed ratio of plasma to gyrofrequency and fixed spectral properties of waves, scattering rates scale as an inverse of magnitude of the magnetic field. We also show that resonant scattering of 10 keV and 100 keV occurs within 10° and 20° latitude of the geomagnetic equator, respectively. At 1 MeV, dominant scattering occurs above 20° latitude. We also present local scattering rates as a function of energy and latitude. Implications of the presented results for the upcoming satellite mission's planning, future measurements, and radiation belt modeling are discussed. Copyright 2009 by the American Geophysical Union.