Kinetic model of the terrestrial ring current.

Abstract

A kinetic model of the ring current-atmosphere interactions (RAM), including losses due to charge exchange, Coulomb collisions, and wave-particle interactions was developed theoretically and implemented numerically. General expressions for quasi-linear diffusion coefficients for energetic particles resonating with EMIC waves were derived, considering the presence of heavy ion components in the plasma, and incorporated in the model. The recovery phase of a typical moderate magnetic storm was studied, using a time-dependent Volland-Stern potential model and a three-dimensional dipole geomagnetic field. Energy and pitch angle measurements of the H$\sp+$, O$\sp+$, and He$\sp+$ ring current populations, supplied by the CHEM spectrometer on the AMPTE/CCE satellite were used as initial conditions. Spatial regions of ion cyclotron wave instability were determined by calculating the convective growth rates of EMIC waves, and selecting regions of maximum wave amplification. Spectral power density of 1 nT$\sp2$/Hz was adopted within the unstable regions according to the new statistical study of Pc 1-2 magnetic pulsations at low L values, obtained by the AMPTE/CCE magnetic field experiment. It was shown that particles with small pitch angles, mirroring deeper into the dense atmosphere, undergo more collisions and are lost faster than particles with larger pitch angles. In addition, late in the storm recovery, the high energy ($>$10 keV) part of the ring current at L = 2-4 is dominated by protons, but the low-energy ($<$10 keV) part is dominated by heavy ions. These results are confirmed by the measurements of the high-energy ring current component, supplied by the CHEM experiment on the AMPTE/CCE spacecraft, and of the low-energy component, supplied by the spectrometers on the ISEE 1 satellite. The energy deposition rate in the plasmasphere was calculated and its magnitude was related to the observed SAR arcs emissions. The generation of ion precipitating fluxes due to different processes was addressed. The inclusion of wave-particle interactions causes significant increase in the values of the ion precipitating fluxes. Fluxes of similar magnitude have been observed, with temporal and spatial evolution in good agreement with our model.