The use of a model current wedge in the determination of the position of substorm current systems

We present a technique for determination of the position and extent of the current systems present during substorm breakup. The parameters of a three-dimensional model of the currents are determined by fitting the model to data from the SAMNET magnetometer array, a midlatitude array of seven stations. The model used is a fully 3D current wedge aligned along dipolar field lines, the parameters being the meridians of upward and downward field-aligned currents (FACs), the latitude of the auroral electrojet and the magnitude of current growth over the observation interval. The method is novel in that the three geometrical parameters are first determined with the fourth arrived at via a secondary process. It has been applied to a number of events and appears to make estimates of the longitudes of the FACs consistent with the predictions of previous methods. Since the method employs a fully 3D model of the substorm current wedge as opposed to an idealised 2D model, it is reasonable to place more reliance on the results so obtained. Moreover, the method also has the additional benefit of a prediction of the latitude of the substorm electrojet and the nature of the current growth through the wedge at substorm onset