An empirical model of the substorm current wedge

Abstract

A wedge‐shaped current linking the nightside ionosphere and the plasma sheet is believed to be the principal cause of a major reconfiguration of the magnetospheric field on the nightside, observed at the onset of the substorm's explosive phase. No dynamical model of the magnetosphere is complete without this important component; however, no realistic representation for the field of the substorm current wedge has been available so far, in part due to the geometrical complexity of that current system and related computational problems. In this work, a simple 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 loops with a spread‐out volume current density. Applying appropriate shift, rotation, and a minor stretching deformation makes it possible to reproduce the desired geometry of the entire system, including field‐aligned currents. The current wedge has a variable longitudinal width, and the model is further generalized by including warping effects due to the tilt of Earth's dipole. This model is intended to be used in data‐based representations of the magnetic field dynamics in the near magnetosphere and will make it possible to reproduce the fast restructuring of the near‐Earth field during the explosive phase of a substorm.