Digital ionosonde observations of the polar cap F region convection

Ground-based drift observations of the winter polar cap F-region show that the magnetospherically induced ionospheric convection can be measured for the bottomside ionosphere. A digital ionosonde with four spaced receiving antennas operated at Thule, Greenland (86° CGL) in the Doppler-drift mode. A number of 24-hour measurements indicate that the drift direction changes linearly as a function of time in accordance with the predicted antisunward convection pattern. The drift velocities vary from 300 to 900 m/s. Measurements at a subauroral station (Goose Bay, Labrador, 65° CGL) with the same spaced-antennas-Doppler-drift technique show a steady westward drift until local magnetic midnight and a fast switch-over at that time to an eastward drift. We conclude that the observed subauroral drifts are the sunward return flows of the polar plasma convection, and the switch-over occurs when the station rotates from the dusk cell into the dawn cell.