Simulations of diffuse aurora with plasma sheet electrons in pitch angle diffusion less than everywhere strong

Abstract

Abstract. To investigate the spatial and spectral structure of the diffuse aurora during a model geomagnetic storm characterized by random impulses in the cross-magnetospheric convection electric field, we simulate the bounce-averaged drift motion and precipitation of plasma sheet electrons. Bounce-averaged drift trajectories are computed from a Hamiltonian formulation in which we have treated the plasma sheet electrons as though they were undergoing strong pitch angle diffusion in Dungey's model magnetosphere (dipole field plus uniform southward Bz). Using the simulation results, we map phase space densities from near the nightside neutral line according to Liouville's theorem, modified to account for particle losses consistent with the postulated pitch angle scattering. We consider three different idealized scattering rate models for the plasma sheet electrons: (1) strong diffusion everywhere, (2) an MLT-independent model for diffusion that is less than everywhere strong, and (3) an MLT-dependent scattering rate model with the same azimuthal average as the MLT-independent model. We evaluate the precipitating energy flux and mean energy at ionospheric altitude h = 127.4 km, as well as the ionospheric Hall and Pedersen conductances, for the three different scattering rate models considered, and we compare the results with each other and with available observations. The limit of everywhere strong pitch angle diffusion yields a simulated diffuse aurora that seems too intense at its maximum

Global aspects of solar wind–ionosphere interactions

“…We imposed a limiting local flux based on the concept from ionospheric theory (Barakat et al, 1987), and the highest fluxes observed in the Strangeway et al (2005) data set. We also realized that the precipitating electron density is closely related to diffuse auroral luminosity, so we used a prescription from Chen and Schulz (2001) who found evidence that pitch angle diffusion is not generally strong enough to fill the loss cone, and has a local time dependence with a peak in the pre-noon sector, again as summarized in Table 1.…”

The Harang reversal and the interchange stability of the magnetotail

“…The conductance consists of two contributions: (i) Solar-EUV-generated conductance that is estimated from the IRI-90 empirical ionosphere driven by F 10.7 and the Ap index and (ii) auroral conductance, which depends on electron precipitation estimated from the Chen and Schulz [2001] MLT-dependent scattering rate model (for more details on the calculation of auroral conductances see Gkioulidou et al [2012]). The conductance consists of two contributions: (i) Solar-EUV-generated conductance that is estimated from the IRI-90 empirical ionosphere driven by F 10.7 and the Ap index and (ii) auroral conductance, which depends on electron precipitation estimated from the Chen and Schulz [2001] MLT-dependent scattering rate model (for more details on the calculation of auroral conductances see Gkioulidou et al [2012]).…”

Transport and loss of the inner plasma sheet electrons: THEMIS observations

“…These investigations suggest that whistler mode chorus waves may be responsible for the loss of the plasma sheet electrons in the morning sector. The scattered electrons precipitate into the atmosphere, and contribute to diffuse auroral emissions in the morning sector [Thomsen et al, 1998;Chen and Schulz, 2001;Newell et al, 2009].…”

“…To obtain the total loss time scales t, we include the effect of the strong diffusion limit, and the expression by Chen and Schulz [2001] is used in the present study. Thus, the electron loss time scale is given as…”