We use results of guiding-center simulations of ion transport to map phase space densities of the stormtime proton ring current. We model a storm as a sequence of substorm-associated enhancements in the convection electric field. Our pre-storm phase space distribution is an analytical solution to a steady-state transport model in which quiet-time radial diffusion balances charge exchange. This pre-storm phase space spectra at L~2-4 reproduce many of the features found in observed quiet-time spectra. Using results from simulations of ion transport during model storms having main phases of 3, 6, and 12 hr, we map phase space distributions from the pre-storm distribution in accordance with Liouville's theorem. We find stormtime enhancements in the phase space densities at energies E~30-160 keV for L~2.5-4. These enhancements agree well with the observed stormtime ring current. For storms with shorter main phases (~3 hr), the enhancements are caused mainly by the trapping of ions injected from open night side trajectories, and diffusive transport of higher-energy (;• 160 keV) ions contributes little to the stormtime ring current. However, the stormtime ring current is augmented also by the diffusive transport of higher-energy ions (E >_ 160 keV) during storms having longer main phases (>_ 6 hr). In order to account for the increase in Dst associated with the formation of the stormtime ring current, we estimate the enhancement in particle-energy content that results from stormtime ion transport in the equatorial magnetosphere. We find that transport alone cannot account for the entire increase in IDstl typical of a major storm. However, we can account for the entire increase in IDstl by realistically increasing the stormtime outer boundary value of the phase space density relative to the quiet-time value. We compute the magnetic field produced by the ring current itself and find that radial profiles of the magnetic field depression resemble those obtained from observational data. 1. Introduction The ring current consists of geomagnetically trapped ions and electrons in the 10-200 keV energy range [e.g., Frank, 1967; Williams, 1981a]. The intensity of the ring current is commonly measured by the geomagnetic index Dst [e.g., Mayaud, 1980, pp. 115-129]. The quiet-time ring current is believed [e.g., Hamilton et al., 1988] to contribute about 10-20 nT to -Dst, but this is mostly offset by magnetopause currents during the geomagnetically quiet intervals which define the baseline (Dst = 0) for the index. Thus the increase in IDstl to -200 nT typically observed during the main phase of a major geomagnetic storm must be associated [cf. Dessler and Parker, 1959; Sckopke, 1966; Carovillano and Maguire, 1966] with about a 10 to 20-fold increase in the energy content of the trapped-particle population.Indeed, large increases in trapped-been observed in connection with major geomagnetic storms. Such particle flux increases extend from L ~ 7 to as low as L-2 and span energies from 1 keV to several hundred keV. However, the main con...

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

Abstract. We employ a three-dimensional ring current model to trace the bounce-averaged drift of singly charged ions during storm-associated enhancements in the convection electric field. Using the simulation results, we map proton phase space density during the main and recovery phases of a storm in accordance with conservation of phase space densityf. We map from an initial quiescent phase space distribution that is obtained by solving the steady state transport equation (bounce-averaged charge exchange balancing bounce-averaged radial diffusion) with observed plasma sheet proton spectra as outer boundary conditions. We obtain proton pitch angle distributions at L -3-4.5 by evaluatingf at representative ring current energies (-20-170 keV). We find that the prestorm and stormtime proton pitch angle anisotropy at any given L between 3 and 4.5 increases with particle energy in agreement with observations. The actual anisotropy at specific energies depends strongly on the shape of the plasma sheet source spectrum at -0.5-3 keV. Relatively large enhancements in the stormtime phase space density from the quiescent distribution occurs at all pitch angles for low energies (

Abstract. In order to understand the characteristics of the quiet time inner plasma sheet protons, we use a modified version of the Magnetospheric Specification Model to simulate the bounce averaged electric and magnetic drift of isotropic plasma sheet protons in an approximately selfconsistent magnetic field. Proton differential fluxes are assigned to the model boundary to mimic a mixed tail source consisting of hot plasma from the distant tail and cooler plasma from the low latitude boundary layer (LLBL). The source is local time dependent and is based on Geotail observations and the results of the finite tail width convection model. For the purpose of selfconsistently simulating plasma motion and a magnetic field, the Tsyganenko 96 magnetic field model is incorporated with additional adjustable ring-current shaped current loops. We obtain equatorial proton flow and midnight and equatorial profiles of proton pressure, number density, and temperature. We find that our results agree well with observations. This indicates that the drift motion dominates the plasma transport in the quiet time inner plasma sheet. Our simulations show that cold plasma from the LLBL enhances the number density and the proton pressure in the inner plasma sheet and decreases the dawn-dusk asymmetry of the equatorial proton pressure. From our approximately force-balanced simulations the magnetic field responds to the increase of pressure gradient force in the inner plasma sheet by changing its configuration to give a stronger magnetic force. At the same time, the plasma dynamics is affected by the changing field configuration and its associated pressure gradient force becomes smaller. Our model predicts a quiet time magnetic field configuration with a local depression in the equatorial magnetic field strength at the inner edge of the plasma sheet and a cross-tail current separated from the ring current, results that are supported by observations. A scale analysis of our results shows that in the inner plasma sheet the magnitude of the Hall term in the generalized Ohm's law is not small compared with the quiet time electric field. This suggests that the frozen-in condition E =-vxB is not valid in the inner plasma sheet and that the Hall term needs to be included to obtain an appropriate approximation of the generalized Ohm's law in that region.

Effects of scattering of electrons from whistler chorus waves and of ions due to field line curvature on diffuse precipitating particle fluxes and ionospheric conductance during the large 17 March 2013 storm are examined using the self-consistent Rice Convection Model Equilibrium (RCM-E) model. Electrons are found to dominate the diffuse precipitating particle integrated energy flux, with large fluxes from~21:00 magnetic local time (MLT) eastward to~11:00 MLT during the storm main phase. Simulated proton and oxygen ion precipitation due to field line curvature scattering is sporadic and localized, occurring where model magnetic field lines are significantly stretched on the night side at equatorial geocentric radial distances r 0 ≳8 R E and/or at r 0~5 .5 to 6.5 R E from dusk to midnight where the partial ring current field has perturbed the magnetic field. The precipitating protons likewise contribute sporadically to the storm time Hall and Pedersen conductance in localized regions whereas the precipitating electrons are the dominate storm time contributor to enhanced Hall and Pedersen conductance at auroral magnetic latitudes on the night and morning side. The RCM-E model can reproduce general features of the Van Allen Probe/MagEIS observed trapped electron differential flux spectrograms over energies of~37 to 150 keV. The simulations with a parameterized electron loss model also reproduce reasonably well the storm time Defense Meteorological Satellite Program integrated electron energy flux at 850 km at satellite crossings from predawn to midmorning. However, model-data agreement is not as good from dusk to premidnight where there are large uncertainties in the electron loss model.