3-DIMENSIONAL RING CURRENT DECAY MODEL

This work is an extension of a previous ring current decay mb;del. In the previous work, a two-dimensional kinetic model was constructed to study the temporal variations of the equatorially mirroring ring curre nt ions, considering charge exchange and Coulomb drag losses along dri ft paths in a magnetic dipole field. In this work, particles with arbi trary pitch angle-are considered. By bounce averaging the kinetic equa tion of the phase space density, information along magnetic field line s can be inferred from the equator. The three-dimensional model is use d to simulate the recovery phase of a model great magnetic storm, simi lar to that which occurred in early February 1986. The initial distrib ution of ring current ions (at the minimum Dst) is extrapolated to all local times from AMPTE/CCE, spacecraft observations on the dawnside a nd duskside of the inner magnetosphere spanning the L value range L = 2.25 to 6.75. Observations by AMPTE/CCE of ring current distributions over subsequent orbits during the storm recovery phase are compared to model outputs. in general, the calculated ion fluxes are consistent w ith observations, except for H+ fluxes at tens of keV, which are alway s overestimated. A newly invented visualization idea, designated as a chromogram, is used to display the spatial and energy dependence of th e ring current ion differential flux. Important features of storm time ring current, such as day-night asymmetry during injection and drift hole on the dayside at low energies (<10 keV), are manifested in the c hromogram representation. The pitch angle distribution is well fit by the function, j(0)(1 + Ay(n)), where y is sine of the equatorial pitch angle. The evolution of the index n is a combined effect of charge ex change loss and particle drift. At low energies (<30 keV), both drift dispersion and charge exchange are important in determining n.