Initial simulation results of storm-time ring current in a self-consistent magnetic field model

The storm-time ring current generates a strong and time-dependent perturbation of the magnetospheric magnetic field (B) over right arrow, and this magnetic-field perturbation can have important feedback on the dynamics of ring current particles themselves. In particular, the modification of (B) over right arrow can significantly alter the gradient-curvature drifts of ring current particles, and the induced electric field associated with partial derivative(B) over right arrow/partial derivative t can inhibit ring current particle injection and energization. Thus in order to accurately simulate the storm-time ring current, a self-consistent magnetic field model that takes these effects into account is needed. This study is our first attempt to address this issue. We assume for simplicity a model for (B) over right arrow such that magnetic field lines lie in meridional planes and satisfy the generic Dungey field line equation. With these two assumptions and given the pressure distribution in the equatorial plane, the force-balanced magnetic field in the equatorial plane is obtained by solving the force balance equation. This force balance equation solver is coupled with our ring current model to provide self-consistent magnetic fields. In this study, we simulate a hypothetical storm with this magnetically self-consistent ring current model. By comparing our simulation results with statistical studies, we find that our model reasonably reproduces the disturbed magnetic field in the equatorial plane in terms of magnitude and location. The equatorial current density shows an inner eastward ring current at similar to 3 R-E, and a outer westward ring current at similar to 4-6.6 R-E, which agrees well with observations. The effects of the self-consistent magnetic field on the dynamics of ring-current particles are discussed. We find that the self-consistent magnetic field tends to prevent ring current particles from deep injection and to mitigate the energization of ring current particles. Thus the ring current simulated in a self-consistent magnetic field model will produce less of a disturbance at the center of the Earth than that simulated in the prescribed dipole or dipole-like magnetic field models without feedback from the ring current.