Auroral activities and long-period geomagnetic pulsations: 1. Pc5 pulsations and concurrent auroras in the dawn sector.

Abstract

It is found that the occurrence and luminosity of diffuse auroras, including pulsating auroras, in the dawn sector show space-time variations synchronized with geomagnetic Pc5 pulsations. The activation region of aurora (not auroral structure) quasi-periodically propagates towards the northwest. The observed propagation velocities at the ionospheric level are about 1km/s northward and about 15km/s westward, respectively. These velocities are in good agreement with the phase velocities of Pc5 pulsations previously measured by radars and by ground networks of geomagnetic field observations. Oscillations in drifts of auroral patches generally in the east-west direction are found to be synchronized with the Pc5 pulsations. The observations suggest that the ground Pc5 pulsations do not necessarily reflect the HM wave structures in the magnetosphere, but the wave nature could be inferred from a close examination of the relationships between the ground magnetic pulsations and concurrent auroral dynamics.