The Magnetospheric Signature of Dayside High Latitude Magnetic Pulsation Events

Pulsations, both impulsive and semi-regular, in dayside high-latitude ground magnetic measurements are by now very well documented. They are signatures of changes to the ionospheric current systems that are directly driven by processes in the outer magnetosphere. The nature of these, however, is still not well understood and neither is the coupling mechanism that connects them to the ionosphere. This study concerns new observational evidence related to this problem. Since the near-Earth phase of the Geotail mission began in late 1994, the spacecraft has obtained measurements from the dayside equatorial magnetosphere (on approximately 30 orbits each year). We mainly utilize data from the low energy particle instrument onboard the spacecraft. Often when the spacecraft is in the dayside magnetosphere impulsive or semi-regular plasma flow oscillations are observed in these measurements. A few case studies have already demonstrated clear correspondence between the magnetospheric flow oscillations and simultaneous ionospheric signatures. We have collected a database of magnetospheric flow oscillation events from 6 years of Geotail data (1995-2000). The preliminary results of analyzing these will be presented here. Main focus will be on their relationship with corresponding ground based magnetic events.