Storm time ring current magnetic field modeling during May 15, 1997 event

When developing a magnetospheric magnetic field model for storm and substorm periods, it is important to adequately represent all current systems that contribute to the total magnetic field. The empirical magnetic field models by Tsyganenko are not well-suited for storm-time field representation: when the ring current in those models is strongly enhanced, the inner tail magnetic field lines become very stretched both on the nightside and on the dayside, which gives a Jupiter-Re shape to Earth's magnetosphere. Here we suggest modeling the ring current with a toroidal current system. This model gives a ring current that is more localized in the radial direction, and more distributed away from the equatorial plane than the current sheet in the Tsyganenko models. The current density distribution in a cross-section of the toroid is a bi-Gaussian distribution, and the toroid itself is constructed using a set of current rings. This representation allows us to vary the parameters, which determine the toroid position, current density distribution and the density of the 3D-ring current distribution grid. The ring current model is incorporated in the Tsyganenko T89 magnetic field model. We examine a well-documented storm event, which occurred on May 1516, 1997 with a Dst-index decrease below 100 nT by 1200 UT on May 15, 1997. We compare the model magnetic field with observations from GOES 8 and 9 satellites. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.