A parametric study on the diffuse auroral precipitation by resonant interaction with whistler mode chorus

Abstract

The diffuse aurora is generally believed to be the result of ∼keV electron precipitation from the magnetosphere, which presents an important sink of magnetospheric particles, a primary high-latitude ionospheric energy source, and a strong magnetosphere-ionosphere coupling mechanism. Resonant scattering of the plasma sheet electrons by electron cyclotron harmonic and whistler mode chorus waves is suggested to be responsible for the diffuse auroral precipitation. The dependence of quasi-linear diffusion rates and consequent diffuse auroral precipitation on the spatial position L, normal angle, and frequency distribution of both upper-band chorus (UBC) and lower-band chorus (LBC) is investigated in detail. Whistler mode chorus waves are found to be more effective in the production of diffuse aurora at larger L shells. The normal angle and frequency distribution of UBC can significantly affect the diffusion rates for ∼keV electrons and the consequent diffuse aurora precipitation. Numerical results show that the strong diffusion limit for ∼keV electrons can be reached up to large pitch angles closer to 90°, and the diffuse auroral precipitation can be remarkably enhanced when the UBC waves possessing a relatively larger normal angle range or centering higher in the band. In contrast, the diffusion rates and diffuse auroral precipitation of electrons with energies E k < 2 keV are largely independent of the normal angle and frequency distribution of LBC waves. Enhanced precipitations of ∼5 keV electrons are found to occur when the LBC waves centering higher in the band. The current results suggest that the significant variability of wave characteristics and the variation with spatial position should be taken into account in order to identify the dominant mechanism for diffuse aurora.