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

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. fn response to t hese boundary perturbations, the antarctic stations South Pole and AGO-PS, located at about the same local time as Interball-1, observed impulsive mag netic variations. These variations were similar;to previously reported magn etic variations observed in the northern hemisphere conjugate region during this event and may be related to discrete field-aligned currents linking t he ionosphere to the perturbed outer magnetosphere. Westward propagation of the magnetic signatures in both ionospheric regions is consistent with a t ravelling convection vortex event; however, the speed is significantly high er in the north (similar to 10 km/s) than in the south (similar to 3 km/s). A localized intensification of energetic electron precipitation (427.8 nm auroral emission and riometer absorption) was observed at South Pole statio n, but not at AGO-P3 or at the nominally conjugate locations in Greenland a nd Canada. The complex, Z-component Variation of the magnetic pulse accompa nying the particle precipitation at South Pole may be evidence of a localiz ed ionospheric conductivity enhancement, as proposed in a recent model stud y of travelling convection vortices.