| Geomagnetic pulsation events with long (100-1000 second) periods that are accompanied by electron precipitation pulsations at the same frequency have been reported at various latitudes. A search of the data from South Pole station for the period from 1982 to 1989 revealed over 200 such events. A comparison of these events with the predictions of Coroniti and Kennel (1970) was undertaken, including examination of VLF data, interplanetary magnetic field data, DMSP satellite data, and data from South Pole's conjugate station at Iqaluit, as well as the riometer and magnetometer data from South Pole used in the original search. Data from the IRIS Imaging Riometer were also used when available. A consideration of the respective wave and particle transit times from the magnetic equator to the ground leads to an expectation that the onset of pulsations in the magnetometer data will lag the onset of pulsations in the riometer data by several minutes. This disparity in onset times, together with VLF modulation in the proper frequency range, serve as important indicators of whether or not an event can be explained by the above-cited theory. While about a third of the events fit the prediction of Coroniti and Kennel, another third cannot be explained by this theory, and possible alternative mechanisms are explored. The remaining third of the events appear at first to be inexplicable in terms of any transit time argument, but analysis of the IRIS data shows that this third class of events arises from differences in the spatial coverage of the instruments. |
