AN EMPIRICAL-MODEL OF THE SUBSTORM CURRENT WEDGE

A wedge-shaped current linking the nightside ionosphere and the plasma sheet is believed to be the principal cause of a major reconfiguratio n of the magnetospheric held on the nightside, observed at the onset o f the substorm's explosive phase. No dynamical model of the magnetosph ere is complete without this important component; however, no realisti c representation for the field of the substorm current wedge has been available so far, in part due to the geometrical complexity of that cu rrent system and related computational problems. In this work, a simpl e and flexible analytical model is proposed for the magnetic field of substorm current wedge. The key element of the mathematical treatment is the vector potential of the field produced by a pair of current loo ps with a spread-out volume current density. Applying appropriate shif t, rotation, and a minor stretching deformation makes it possible to r eproduce the desired geometry of the entire system, including field-al igned currents. The current wedge has a variable longitudinal width, a nd the model is further generalized by including warping effects due t o the tilt of Earth's dipole. This model is intended to be used in dat a-based representations of the magnetic field dynamics in the near mag netosphere and will make it possible to reproduce the fast restructuri ng of the near-Earth held during the explosive phase of a substorm.