Efficient diffuse auroral electron scattering by electrostatic electron cyclotron harmonic waves in the outer magnetosphere: A detailed case study

Abstract

This paper is a companion to a paper by Liang et al. (2011) which reports a causal connection between the intensification of electrostatic ECH waves and the postmidnight diffuse auroral activity in the absence of whistler mode chorus waves at L = 11.5 on the basis of simultaneous observations from THEMIS spacecraft and NORSTAR optical instruments during 8-9 UT on February 5, 2009. In this paper, we use the THEMIS particle and wave measurements together with the magnetically conjugate auroral observations for this event to illustrate an example where electrostatic electron cyclotron harmonic (ECH) waves are the main contributor to the diffuse auroral precipitation. We use the wave and particle data to perform a comprehensive theoretical and numerical analysis of ECH wave driven resonant scattering rates. We find that the observed ECH wave activity can cause intense pitch angle scattering of plasma sheet electrons between 100eV and 5keV at a rate of >10-4s-1 for equatorial pitch angles eq < 30. The scattering approaches the strong diffusion limit in the realistic ambient magnetic field to produce efficient precipitation loss of