Search for: All records

In the Earth's radiation belts, an upper limit on the electron flux is expected to be imposed by the Kennel-Petschek mechanism, through the generation of exponentially more intense whistler-mode waves as the trapped flux increases above this upper limit, leading to fast electron pitch-angle diffusion and precipitation into the atmosphere. Here, we examine a different upper limit, corresponding to a dynamical equilibrium in the presence of energetic electron injections and both pitch-angle and energy diffusion by whistler-mode chorus waves. We first show that during sustained injections, the electron flux energy spectrum tends toward a steady-state attractor resulting from combined chorus wave-driven energy and pitch-angle diffusion. We derive simple analytical expressions for this steady-state energy spectrum in a wide parameter range, in agreement with simulations. Approximate analytical expressions for the corresponding equilibrium upper limit on the electron flux are provided as a function of the strength of energetic electron injections from the plasma sheet. The analytical steady-state energy spectrum is also compared with maximum electron fluxes measured in the outer radiation belt during several geomagnetic storms with strong injections, showing a good agreement at 100–600 keV.