Direct determination of large‐scale magnetospheric field‐aligned currents with SuperDARN

The SuperDARN (SuperDual Auroral Radar Network) radars measure large‐scale 2D images of the plasma convection velocity v in the high‐latitude F‐region. From the 2D convection maps, plasma flow vorticity can be directly calculated. We show that the vorticity is a direct measure of J_m/Σ_P, the “magnetospheric” component J_m of the field‐aligned current (FAC) per unit height‐integrated Pedersen conductivity Σ_P. The maps of J_m/Σ_P show clearly the Region 0, 1, and 2 currents, uncontaminated by the “ionospheric” FAC component J_i caused by ionospheric Pedersen and Hall conductivity gradients (which are important in the nightside substorm sector). The generation of the large‐scale magnetospheric FAC images of J_m/ Σ_P from the SuperDARN convection vorticity is explained and examples of dayside FAC patterns for northward and southward IMF conditions are presented for the SuperDARN radar pair in Canada at Saskatoon and Kapuskasing. By summer, 1995, FAC images will be available from three northern hemisphere SuperDARN radar pairs, with a field‐of‐view extending over some 12 hours MLT (from western Canada to Scandinavia), and from one Antarctic radar pair.