No abstract

The results of an analysis of 16 Pi 2 pulsations observed with an extended east-west chain of midlatitude, ground-based magnetometers are reported. The events were chosen such that the center of the substorm current system, defined by using the midlatitude bays associated with these pulsations, was within the longitudinal extent of the station chain. A current wedge model is also used to interpret the observed polarization pattern of the Pi 2 pulsations. This pattern is used to locate the center of the Pi 2 current system. The centers of the Pi 2 and substorm current systems occur at the same meridian for only -65% of the events. This result suggests that the Pi 2 current system and the substorm current wedge are not always the same. The longitudinal extent of the Pi 2 current system estimated from the Pi 2 polarization pattern averages --•90 ø or -6 hours local time for the events in the study. The sense of ellipticity of the waves, anticlockwise looking down the field line in the northern hemisphere, agrees with previous results from these latitudes. Estimates of the wave-phase difference between stations show that, in general, the eastern station of a station pair leads the western one at all local times for both H and D components. When plotted in a substorm coordinate system based on the mid-latitude bay, the phase difference per degree of longitude shows a tendency to decrease in the eastern portion of the current wedge. This longitudinal pattern of phase difference is consistent with the eastern, downward, field-aligned currents being less localized than the western, upward, field-aligned currents. , 1980], the predominant observation is that eastern stations lead in phase. This result has been interpreted as western phase propagation on the entire nightside. Since no physical interpretation consistent with substorm models has been developed, we concluded that a further study of phase variations was warranted. Our results confirm that eastern stations lead in phase, but that the phase variation is not uniform across the substorm current wedge.The following section describes the magnetometer array and data set used. We then describe the model of the substorm current wedge and the associated, predicted Pi 2 polarization pattern. Examples of Pi 2 pulsations, their polarization pattern, and the related bay structure are then given. The polarization pattern is described for 16 events where it is possible to locate the center of the substorm 7958

No abstract

No abstract

No abstract