The Magnetospheric Signature of Dayside High Latitude Magnetic Pulsation Events

Dr. Therese Moretto
Senior Research Associate (National Research Council)
NASA, Goddard Space Flight Center

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 talk 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. These results will be presented and discussed in some detail. Currently, we are collecting a database of such magnetospheric flow oscillation events from many years of Geotail data (1995-2000). The talk will present also preliminary results of this effort.