A new model of field‐aligned currents derived from high‐precision satellite magnetic field data

Abstract

A model of field‐aligned currents is derived from high‐precision magnetic field measurements from the Ørsted and Magsat satellites, being parameterized by the interplanetary magnetic field strength and direction for summer, winter and equinox. The high‐precision data allow the model to be determined directly by a simple 2‐D curl technique combined with fitting of spherical harmonic functions. New elements of the model are: (a) the FAC patterns are determined separately for both polar regions, resolving the seasonal dependence of interhemispheric asymmetries, (b) the IMF ∼ 0, ground‐state patterns are also resolved; these elements are obtained for the first time. From the model, the total upward/downward currents have been determined for various IMF conditions. The ratio of the summer/winter currents is ∼1.35 and the equinox currents ∼1. The model allows FAC mapping for IMF | B | ≤ 12 nT, except during magnetic storms and substorms.