PC-5 ULF WAVES OBSERVED SIMULTANEOUSLY BY GOES-7 AND THE CANOPUS MAGNETOMETER ARRAY

Applying pure state filtering techniques to 1 month (March 1990) of GO ES 7 and CANOPUS (Canadian Auroral Network for the OPEN Program Unifie d Study) magnetometer data, we have detected several dominantly compre ssional Pc 5 events in the satellite data which were well correlated w ith the pulsation signal recorded by the ground stations. On the groun d, near the GOES 7 magnetic footprint, these pulsations were seen with polarization characteristics similar to those observed at geosynchron ous orbit, i.e., without ionospheric rotation of the transverse polari zation major axis. Using data from 13 stations of the CANOPUS array, w e show that these compressional wave events seen by GOES 7 at L = 6.67 were associated with field line resonances (FLRs) at higher L values (L greater than or equal to similar to 8), propagating antisunward wit h small azimuthal wave numbers. Besides these compressional waves, we identified a number of azimuthally (east-west) polarized transverse Pc 5 events at geostationary orbit. Near the subsatellite point these ap peared on the ground with the polarization major axis aligned in about the north-south direction, i.e., rotated through similar to 90 degree s between magnetosphere and ground. The spatial characteristics, as de rived from the ground array data, show that these transverse events re present FLRs on or near the satellite's L shell. By means of selected events with clear FLR characteristics in the CANOPUS data, we determin e the resonance position from the ground array data and examine the va riation of the signal characteristics at geosynchronous orbit with inc reasing radial distance of GOES 7 from the resonant field line. We fin d that the transverse wave characteristics, dominant near the resonanc e; decay on relatively small-scale lengths and are transformed into co mpressional wave characteristics within about 1-2 R(E) from the resona nce position. The diurnal variation of the signal parameters for these events suggests that compressional Pc 5 waves at geosynchronous orbit associated with FLRs at L > 8 are preferentially generated near local noon. Finally, via consideration of solutions of the uncoupled toroid al mode wave equations based on the observed signal frequencies and re sonance positions, we discuss the held-aligned harmonic of these reson ances.