Modeling the ring current magnetic field during storms

[1] We present a new model for the inner magnetosphere ring current to get a realistic representation of the magnetic field during storm times. We use a bean-shaped current system, which has cross section that is close to the observed distribution of trapped particles in the inner magnetosphere. The model is symmetric both longitudinally and in the north-south direction, and the current density in the radial direction varies as a Gaussian. The latitudinal distribution of the current density is specified by an "anisotropy index,'' which is zero for a particle distribution that is isotropic along field lines. Increasing the anisotropy index gives a particle distribution concentrated closer to the equator. We use this method to model the magnetic field evolution during two geomagnetic storms: one on May 2, 1998, when Dst reached -80 nT, and the other on May 15, 1997, when it reached -120 nT. The ring current in the Tsyganenko (T89) magnetic field was replaced by our new ring current representation, and the model free parameters are specified using observations from GOES and Polar satellites and Dst measurements for each time step separately. We discuss the field configuration changes during the storm, and we evaluate the capability of our modeling technique to represent the large-scale magnetospheric configuration during storm periods.