Electron Precipitation Associated with Dayside Ionospheric Traveling Convection Vortices

Electron precipitation, inferred from photometric and riometer observations at South Pole, has been examined for two ground magnetic perturbation events. These events exhibit the characteristics of traveling ionospheric convection vortices, as determined from Greenland magnetometer chain data. One of the cases occurred about 45 min past noon and appears to have been initiated by a change in the x-y plane orientation of the IMF unaccompanied by any change in the solar wind dynamic pressure. The origin of the second event, which occurred about 1 hr. prior to noon, is uncertain at this time. The pre-noon event was observed with the imaging riometer at South Pole, which detected a small-scale absorption region moving westward (tailward) with an average speed of 1-3 km/s. The most intense particle precipitation in both events was associated with the leading vortex, that generated by the downward FAC, of the two-cell system.