Non-linear whistler mode wave effects on magnetospheric energetic electrons

Abstract

Electron energy transport due to nonlinear plasma-wave and particle interactions is carried out by waves and particles resonating with each other. Many previous nonlinear wave studies have only considered the main resonance between waves and electrons, since the contributions from other resonant orders were ignored as insignificant. We have found through test particle simulations, however, that although independent separate contributions from higher-order resonances can be small, they can have a rather significant impact on the main-order contribution and hence on the total nonlinear wave effects. Contributions from different orders can interfere with each other and the overall nonlinear wave effect is significantly different from that of just the major resonance. Therefore, in the nonlinear wave/particle interaction regime, contributions from different resonant orders are inseparable and contributions from higher order wave–particle resonances should all be included. Similarly, banded plasma waves should be used in nonlinear wave studies instead of assuming monochromatic waves. When the essential factors mentioned above are included, the overall electron transport due to the nonlinear plasma wave effects takes the form of a diffusion-like process, rather than advection, as reported in many previous studies. It is also found that electron transport induced by whistler mode waves is an important mechanism for the formation of the electron butterfly pitch-angle distribution.