Time dependence of heavy ion concentration in the ring current

The focus of this project was a comprehensive study of processes responsible for the decay of the storm time ring current. We have examined ring current ion loss from interaction with waves in the Pc 1 (Hz) and Pc 5 (mHz) frequency ranges, since such waves are a common feature of the ring current region during recovery from magnetic storms. Pc 1 waves, identified as electromagnetic ion cyclotron (EMIC) waves, are generated by the loss cone distribution of ring current ions. Both linear dispersion analysis and particle simulations show the importance of the loss cone vs. bi-Maxwellian nature of ring current ion distributions in determining the growth rate, angle of propagation, and polarization of EMIC waves. Pitch angle diffusion is found to be an important loss process for ring current H(+). Compressional Pc 5s are found to contribute to ring current 0(+) loss. Their frequency (2-5 mHz) is comparable to the bounce frequency of ring current 0(+). We have performed ring current test particle simulations in prescribed wave and background fields, including a dipole magnetic convection and corotation electric field. We find that a drift-bounce resonant interaction causes ring current 0+ loss to the magnetopause in the energy range of a few tens of keV for moderate kp (1.5-2).