The effect of geomagnetic activity on north polar currents in winter

Average north polar currents for the winter season have been derived from geomagnetic hourly means at six levels of geomagnetic activity. The twin-vortex pattern, normally associated with more disturbed conditions, persisted even on the quietest (mean Ap ≈ 1) days. When Ap increased to 24, the Harang discontinuity appeared earlier by about 3.5 h, though the current system as a whole remained unchanged in orientation. The average quiet day seems to be associated with a weak IMF oriented northwards and towards the Sun, with a low solar wind velocity and low proton temperature.