Observed correlations between interplanetary magnetic field variations and the dynamics of the auroral oval and the high-latitude ionosphere

Flights of the Air Force Cambridge Research Laboratories flying ionospheric laboratory investigated the day sector of the auroral oval under conditions of darkness. Airborne all-sky cameras and a vertical incidence ionospheric sounder were used to follow the time history of the equatorward boundary of the auroral oval and the F layer irregularity zone (Fliz). In the geomagnetic day sector the Fliz and the discrete auroras are most probably produced by precipitation of particles through the cusp. Meridional motions of the equatorward boundary of the auroral oval and the Fliz were observed to correspond to variations in the interplanetary magnetic field (IMF). Time delays of about 10–30 min between a southward turning of the IMF, measured by Explorer 35 at 60 RE, and the beginning of an equatorward shift of the oval and the Fliz are typical. By combining auroral all-sky camera data from the aircraft with auroral all-sky camera data from the Alaskan meridian chain of stations, which is located in a time sector different from that of the aircraft, we can show that equatorward shifts of the auroral oval can occur over a broad longitudinal (local time) extent. Therefore the size of the auroral oval has a direct dependence on the IMF. Discrete auroras were always seen following a southward turning of the IMF, whereas in some instances, discrete auroras weakened in intensity or disappeared following a northward turning of the IMF.