Ionospheric flows associated with a transpolar arc

Data on plasma flows associated with a transpolar arc are obtained by combining observations (on January 21, 1982) from the auroral imaging instruments aboard the DE 1 spacecraft with simultaneous observations of ionospheric electron drift velocities obtained with a ground-based coherent radar system and with an ion-drift meter on the DE 2 spacecraft at about 800-km altitude. The combined observations demonstrate that the electron-drift velocities within the transpolar arc at the intersection with the auroral oval on the nightside are directed equatorward into the oval and that the transpolar arc connects to the oval near the Harang discontinuity. It is also shown that the sunward flow along the transpolar arc is present near local noon.