Pi 2 pulsations are often used to indicate the start of the substorm expansion phase. In this report the relationship between the Pi 2 polarization pattern observed at a mid-latitude longitudinal chain of stations and synchronous orbit magnetic activity is explored. Eighteen single and multiple-substorm-onset intervals, consisting of 55 Pi 2's, are examined using data from the Air Force Geophysics Laboratory Magnetometer Network and the synchronous orbit satellites GOES 2 and 3. Magnetic fluctuations at synchronous orbit are found to be enhanced when the satellite is near the Pi 2 pattern center, defined as the longitude where the major axis of the polarization ellipse is along the H axis. The pattern center is also observed to separate regions of dipolarization and more taillike magnetic signatures. East of the pattern center the field inclination becomes larger, i.e., more dipolelike, while west of the center the field inclination becomes smaller, i.e., more taillike. Although regions of substorm activation, as determined by the Pi 2 pattern, move between onsets during multiple-onset events, no consistent azimuthal motion was found. |