Origin of flat-top electron distributions at the Earth’s bow shock

Abstract

ABSTRACT An explanation is provided for flat-top electron distributions observed at the bow shock. It is shown that flat-tops are produced by the stochastic wave energization (SWE) mechanism. First, we demonstrate that flat-tops in one-dimensional (1D) reduced distribution functions correspond to rings in 2D distribution functions, or to shell distributions in 3D. The velocity of the ring/shell corresponds to the E × B velocity due to the wave electric field, $V_{\mathrm{ E}{\times }\mathrm{ B}}=\tilde{E}_\perp /B$, which is a natural consequence of the SWE process. The identification of processes responsible for electron flat-top distributions was made with magnetospheric multiscale measurements supported by test-particle simulations.