Quantitative ring current model: Overview and comparison with observations

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This paper describes a new quantitative ring current model that solves temporal evolution of the ion distribution in the magnetosphere by tracing the ion drift motion. The plasma sheet density as a boundary condition of our model depends on the solar wind density. The tracing is performed under a dipole magnetic field and a time-dependent convection electric field depending on the solar wind parameters. The ions are lost by two processes; the charge exchange with neutral hydrogen and the convection outflow due to encounter with the dayside magnetopause. Magnetic disturbance is directly derived from the calculated current density with the three- dimensional Biot-Savart integral; this is a new simulation method. Using this model, we have examined the physical mechanism of the storm-time ring current responding to the interplanetary parameters. We simulated three successive storms which occurred in April 1997 as a case study. The following subjects concerned with dynamics of the ring current were examined; (1) the causes of the ring current development, (2) the electric current distribution, (3) the effects of the charge exchange loss, (4) the energy composition of the plasma pressure, (5) the response time lag of the plasma sheet density variation to the solar wind density and (6) the diamagnetic effect.
国立極地研究所の論文