Physics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsm33b..02c&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #SM33B-02
Physics
7230 Seismicity And Seismotectonics, 7843 Numerical Simulation Studies, 2778 Ring Current, 2788 Storms And Substorms
Scientific paper
We simulate the three dimensional structure of the ring-current magnetic field by tracing the guiding centers of representative ions and electrons from the plasma sheet as they bounce between mirror points and drift across B in 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 ≥ 2) throughout this model magnetosphere. We trace bounce-averaged drifts for ions and electrons conserving their first two adiabatic invariants m and J (with values that correspond to energies ˜ 10 - 300 keV at L = 3). Using these simulation results, we map phase space densities according to Liouvilleês theorem but taking into account losses due to charge exchange for protons and losses due to wave-particle interactions for electrons. 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 particle data to the boundary of our model magnetosphere. From the simulated phase-space densities, we calculate the particle pressure and energy density distributions. From the pressure distributions, we compute the ring current magnetic field. From simulations of the 19 October 1998 storm, we find that the large AMIE electric field in the evening sector would have led to rapid ( ˜ 20 minutes) inward transport of plasmasheet ions from the neutral line to L ˜ 3 near the dusk meridian. We can thus account for the observed rapid formation of the partial proton 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 Earthês ambient magnetic field. This suggests a future need for eventually calculating particle transport in a magnetically self-consistent model.
Chen Margaret W.
El-Alaoui Mostafa
Liu Shujuan
Lu Gang
Lyons Larry R.
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