Fig. 2.

Current model used for inversion. Currents 1 … N _C shown following lines of constant quasi-dipole latitude, with the satellite crossing the magnetic equator (shown as current j). Origin O represents the Earth’s center with vector r _jk pointing to linear current segment k of arc current j, and r _i pointing to satellite observation point i. Unit current vector I _jk shown in enlarged region with relevant parameters (see text). Basis vectors and are shown for use during the modeling step (Section 7).