Rapid acceleration of radiation belt energetic electrons by Z‐mode waves

Abstract

We present the first simulation of the effect of Z‐mode waves on the outer radiation belt electron dynamics. We calculate bounce‐averaged diffusion rates in pitch angle and momentum and then use them as inputs to solve a 2‐D momentum‐pitch angle diffusion equation. Numerical results show that the phase space density (PSD) of 1 MeV electrons can enhance substantially and very rapidly (e.g., 30 minutes). In particular, the momentum diffusion rate exceeds the pitch angle and cross diffusion rates at 0.5 MeV and above, a behavior completely different from that for EMIC and chorus waves. Consequently, momentum (instead of pitch angle or cross) diffusion plays a dominant role in the dynamic evolution of energetic electrons. Moreover, the PSD evolution is found to be very dependent upon the assumed initial particle distributions. These results provide further insights on the interplay between acceleration mechanisms of outer radiation belt electrons.