HR: 09:40h
AN: SH51A-07    [PDF]
TI: Simulated Radial and Azimuthal Structure of Proton Ring-Current Field
AU: * Chen, M W
EM: mchen@aero.org
AF: Space Science Applications Laboratory, The Aerospace Corporation, P. O. Box 92957, M2-260, Los Angeles, CA 90009-2957 United States
AU: Schulz, M
EM: mike.schulz@lmco.com
AF: Lockheed Martin Advanced Technology Center, O/L9-42, B/255 3251 Hanover Street, Palo Alto, CA 94304 United States
AU: Lu, G
AF: High Altitude Observatory, NCAR, Boulder, CO 80307
AU: Lyons, L R
EM: larry@atmos.ucla.edu
AF: Department of Atmospheric Sciences, UCLA 405 Hilgard Avenue, Los Angeles, CA 90095-1567 United States
AU: El-Alaoui, M
EM: mostafa!@igpp.ucla.edu
AF: IGPP, UCLA 405 Hilgard Avenue, Los Angeles, CA 90096-1567 United States
AU: Thomsen, M
EM: mthomsen@lanl.gov
AF: Los Alamos National Laboratory, MS-D466, Los Alamos, NM 87545 United States
AB: We simulate the radial and azimuthal structure of the proton ring-current magnetic field by tracing the guiding centers of representative ions from the plasma sheet as they drift within a model magnetosphere. The ambient magnetic field model we use for this study is the Dungey model, which consists of a dipole field plus a uniform southward ``tail'' field. We map a spatially analytical expansion of the AMIE ionospheric electric potential, expressed as a function of magnetic latitude and magnetic local time, along magnetic field lines (for $L \ge 2$) throughout this model magnetosphere. We trace the bounce-averaged drift for ions conserving the first two adiabatic invariants $\mu$ and $J$ (with values that correspond to energies of $\sim10 -300$ keV at $L = 3$). Using these simulation results, we map proton phase space densities according to Liouville's theorem but taking into account losses due to charge exchange. We specify an ``initial'' proton ring current distribution by solving the steady-state transport equation that balances quiescent radial diffusion against charge exchange. To obtain MLT-dependent and UT-dependent boundary values for our phase space density distribution, we map geosynchronous LANL ion data to the boundary of our model magnetosphere as boundary conditions. From the simulated phase-space density, we calculate the proton pressure and energy density distributions. From the pressure distributions, we compute the separate contributions of the magnetic field perturbation from the gradient-curvature drift currents, magnetization currents, and field-aligned currents needed to satisfy Ampere's law. We add these contributions together to obtain the total ring current magnetic field. We perform simulations for a few storm events including the 19 October 1998 storm. We find that during the 19 October 1998 storm the large AMIE electric field in the evening sector would have led to rapid ($\sim 20$ minutes) inward transport of ions from the plasma sheet to the dusk meridian at $L \sim 3$. We can thus account for the observed rapid formation of the partial ring current there and its subsequent symmetrization to a wider range of MLT. In regions where the ring current is especially intense, the ring current magnetic field can be a significant fraction of the Earth's magnetic field. This suggests a need for eventually calculating the particle transport in a magnetically self-consistent model in the future.
DE: 2708 Current systems (2409)
DE: 2730 Magnetosphere--inner
DE: 2753 Numerical modeling
DE: 2778 Ring current
DE: 2788 Storms and substorms
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting