A dayside ionospheric absorption perturbation in response to a large deformation of the magnetopause

Abstract

A large deformation of the dayside magnetopause was observed by Interball-1 from 1132 to 1139 UT on July 24, 1996. The spacecraft, near 0800 LT at the time, transited the magnetosheath twice within 7 minutes. In response to these boundary perturbations, the antarctic stations South Pole and AGO-P3, located at about the same local time as Interball-1, observed impulsive magnetic variations. These variations were similar to previously reported magnetic variations observed in the northern hemisphere conjugate region during this event and may be related to discrete field-aligned currents linking the ionosphere to the perturbed outer magnetosphere. Westward propagation of the magnetic signatures in both ionospheric regions is consistent with a travelling convection vortex event; however, the speed is significantly higher in the north (∼ 10 km/s) than in the south (∼ 3 km/s). A localized intensification of energetic electron precipitation (427.8 nrn auroral emission and riometer absorption) was observed at South Pole station, but not at AGO-P3 or at the nominally conjugate locations in Greenland and Canada. The complex, Z-component variation of the magnetic pulse accompanying the particle precipitation at South Pole may be evidence of a localized ionospheric conductivity enhancement, as proposed in a recent model study of travelling convection vortices.