Comparisons of Plasmaspheric Hiss and Lightning-generated Whistler Wave Electron Pitch Angle Diffusion Models

Abstract:

Two of the largest contributors to electron pitch angle diffusion in the plasmasphere are plasmaspheric hiss and lightning-generated whistler mode waves. Several modeling efforts have been made to describe the interaction between electrons and waves associated with these natural processes, most notably by Abel and Thorne [1998] and Meredith et al [2007,2009]. We present an additional lightning-generated whistler diffusion model based on the recent VLF spectral density climatology of Colman and Starks [2013]. Monthly averages of the wave power distribution used to develop this model are provided. A polynomial fit to the spectral intensity profiles is used to describe the power distribution instead of the normal Gaussian formalization. Comparisons between these models are facilitated via a program based on quasi-linear theory, using input parameters that are representative of each model. Diffusion coefficients are presented as a function of equatorial pitch angle and L-shell for L-shells in the range 2.5-4.0 at electron energies of 0.1, 0.5, 1.0, and 5.0 MeV. The diffusion coefficients are applied to the CRRESELE radiation belt model to determine electron loss timescales. The diffused electron flux pitch angle distributions are presented for CRRESELE energies of 0.65, 2.0, 3.15, and 5.75 MeV and at elapsed times of 30 days, 90 days, 1 year, and 4 years after the start of diffusion. Our results are found to be consistent with prior modeling determinations for small wave normal angle propagation, but less diffusive for large wave normal angles.