Statistical Average Estimates of High Latitude Field-aligned Currents from the Stare and Sabre Coherent Vhf Radar Systems

Two bistatic VHF radar systems, STARE and SABRE, have been employed to estimate ionospheric electric fields in the geomagnetic latitude range 61.1 69.3 (geographic latitude range 63.8 72.6) over northern Scandinavia. 173 days of good backscatter from all four radars have been analysed during the period 1982 to 1986, from which the average ionospheric divergence electric field versus latitude and time is calculated. The average magnetic fieldaligned currents are computed using an AE-dependent empirical model of the ionospheric conductance. Statistical Birkeland current estimates are presented for high and low values of the Kp and AE indices as well as positive and negative orientations of the IMF Bz component. The results compare very favourably to other ground-based and satellite measurements.