A 2-DIMENSIONAL ARRAY STUDY OF LOW-LATITUDE PC 5 GEOMAGNETIC-PULSATIONS

Data obtained from the Australia Wide Array of Geomagnetic Stations (A WAGS) have provided a unique opportunity to investigate the spatial va riation of long-period (Pc 5) ULF wave signal characteristics as a res ult of plasma waves in low latitudes. Pure state filtering techniques were applied in order to detect highly polarized Pc5 events and derive the wave signal parameters, i.e., the wave frequency, amplitude, pola rization, and phase. The results indicate that the Pc 5 signal frequen cy was virtually independent of latitude and longitude, while the ampl itude decreased considerably toward lower latitudes. The spatial varia tion of the signal polarization was found to be small. However, a stat istical analysis of the signal polarization revealed a systematic diur nal variation. Counterclockwise sense of rotation (viewed in the direc tion of the ambient magnetic field) with the major axis of the polariz ation ellipse in the northeast quadrant was observed in the local morn ing, while clockwise sense of rotation with the polarization major axi s aligned mainly in the north-south direction was seen in the local af ternoon. Interstation phase analysis yielded small phase variations ac ross the entire station array, indicating azimuthal wave numbers of 1 < m < 3. The signals appeared to propagate westward in the local morni ng sector, while eastward propagation prevailed in the local afternoon . The latitudinal phase variation was also very small, showing signals virtually in phase or with the lower-latitude stations leading slight ly. These observations appear to be consistent with the magnetic groun d signature of global compressional modes or large scale-cavity resona nces trapped in the magnetosphere.