A new diffusion matrix for whistler mode chorus waves
Global models of the Van Allen radiation belts usually include resonant wave-particle interactions as a diffusion process, but there is a large uncertainty over the diffusion rates. Here we present a new diffusion matrix for whistler mode chorus waves that can be used in such models. Data from seven satellites are used to construct 3,536 power spectra for upper and lower band chorus for 1.5 ≤ L∗ ≤ 10, MLT, magnetic latitude 0o ≤ |λm| ≤ 60o and five levels of Kp. Five density models are also constructed from the data. Gaussian functions are fitted to the spectra and capture typically 90% of the wave power. The frequency maxima of the power spectra vary with L∗ and are typically lower than that used previously. Lower band chorus diffusion increases with geomagnetic activity and is largest between 21:00 and 09:00 MLT. Energy diffusion extends to a few MeV at large pitch angles > 60o and at high energies exceeds pitch angle diffusion at the loss cone. Most electron diffusion occurs close to the geomagnetic equator (< 12o). Pitch angle diffusion rates for lower band chorus increase with L∗ and are significant at L∗ = 8 even for low levels of geomagnetic activitywhile upper band chorus is restricted to mainly L∗ < 6. The combined drift and bounce averaged diffusion rates for upper and lower band chorus extend from a few keV near the loss cone up to several MeV at large pitch angles indicating loss at low energies and net acceleration at high energies.
Authors: Horne, Richard B., Kersten, Tobias, Glauert, Sarah A., Meredith, Nigel P., Boscher, Daniel, Sicard-Piet, Angelica, Thorne, Richard M., Li, Wen