Diffuse auroral electron scattering by electrostatic electron cyclotron harmonic waves in the dayside magnetosphere

Although electrostatic electron cyclotron harmonic (ECH) waves are frequently observed in the dayside magnetosphere, their effects on the formation of dayside diffuse aurora remain poorly understood. In this study, we quantitatively evaluate the efficiency of dayside ECH wave scattering in producing the electron diffuse aurora precipitation during a typical ECH wave event by calculating the quasi-linear bounce-averaged scattering rates. We find that dayside ECH waves can efficiently pitch angle scatter diffuse auroral electrons on timescales of a few hours to ~1 day over a broad range of electron energy and equatorial pitch angle, i.e., from ~300 eV to 10 keV with a_eq from the loss cone to 45°. Especially for ~300 eV to 2 keV electrons, the scattering rates can even approach the strong diffusion limit, resulting in an almost fully filled loss cone. Our results confirm the significant role of ECH waves in driving the dayside diffuse aurora.