Auroral activities and long-period geomagnetic pulsations: 2. Ps5 pulsations following auroral breakup in the premidnight hours.:2. Ps5 Pulsations Following Auroral Breakup in the Premidnight Hours

Bright auroral forms several hundreds of km in spatial extent were observed repeatedly (a few to about 15min, periodicity) in the premidnight hours, following auroral breakups. The auroral forms drifted towards the northwest or the southwest, and were related to the magnetic field fluctuations on the ground in a similar period range. The leading front of the drifting auroral form has a discrete auroral (vortexchain) feature. After the passage of discrete forms pulsating aurora appears. From the comparison with magnetic field perturbations at the geosynchronous orbit satellites GOES 5 and GOES 6, these auroral forms are likely to correspond to the depression of the magnetic total intensity. A possible source of these bright auroral forms is hot plasmas injected from the plasma sheet. The concurrent magnetic pulsations, here called Ps5, would be produced by the fluctuating electric field and conductivity in the ionosphere due to the electron precipitation into the auroral forms. Hot plasma clouds, quasi-periodically injected during the course of a substorm, are related to the auroral and magnetic field pulsations. A steep injection front of hot plasma in the magnetosphere is likely related to discrete auroras at the ionosphere.