Comparison of high-latitude ionosonde drifts with a convection model

A comparison of averaged ionospheric F-region drifts measured by a digital ionosonde at Casey, Antarctica is made with convection patterns from the Weimer (1995) electric potential model. Significant changes occur in the average diurnal flow vectors over Casey as the Interplanetary Magnetic Field angle in the By-Bz plane is varied. Steps of 30° in By-Bz angle show the evolution of the measured convection as Bz turns from southward to northward through ± By. This results in drifts that vary respectively from anti-sunward to sunward on the dayside. These changes compare favourably with the Weimer patterns as the two-cell pattern distorts and forms a three- and four-cell pattern when the IMF is respectively within ∼60° and ∼30° of Bz due north. At most IMF angles, drift directions are usually within 20° and speeds within 100 m/s of the model predictions. The best direction/speed agreement do not coincide at one IMF angle, being mostly dependent on the strength of flows and the position of convection cell centers.