Dominant Roles of High Harmonics on Interactions Between AKR and Radiation Belt Relativistic Electrons

Auroral kilometric radiations (AKR) are widely existing superluminous waves in the magnetosphere. Due to rarely available measurements of AKR magnetic field components, we derive the explicit expression of diffusion coefficients in terms of electric field components, which can be applied to various space plasma waves. Using Van Allen Probes data, we calculate diffusion coefficients with different harmonic orders for two AKR events. It is found that the first (higher) harmonic order contributes to diffusion coefficients at small (larger) pitch angles. The effect of higher harmonic orders becomes more significant as the electron energy increases. These results are contrary to the case of chorus wave, in which the first order usually contributes much to wave-particle interactions. Estimations show that the phase space density of 0.5 MeV electrons can increase similar to 10 times within 6 hr by AKR. This study is important for better modeling of AKR-induced radiation belt electron dynamics.