A statistical study on characteristics of high latitude Pi 3 pulsations

The latitude and magnetic local time distributions of Pi 3 pulsations relative to polarization and the position of maximum intensity are presented using data from the high-latitude North American International Magnetospheric Study magnetometer network. These distributions are compared with those of Pc 5 and Pi 2 pulsations. The locus of Pi 3 maximum amplitude and the corresponding curve for Pc 5 are similar in general shape, but the former is located at considerably lower geomagnetic latitudes than the latter. For Pi 2 pulsations, the latitude of maximum amplitude is found to agree well with the auroral oval, whereas the locus of Pi 3 amplitude maximum deviates from the auroral oval appreciably in the dawn and dusk regions and is near the poleward border of the auroral oval in the premidnight region where the equatorward boundary of the oval is lowest in latitude. It is concluded that dayside Pi 3 pulsations may have a different generation mechanism from that for nightside Pi 3 events.