A COMPARISON BETWEEN PC-3-4 PULSATIONS OBSERVED BY GOES-7 AND THE CANOPUS MAGNETOMETER ARRAY

We have analyzed 1 month of GOES 7 and Canadian Auroral Network for th e OPEN Program Unified Study (CANOPUS) magnetometer data and compared Pc 3-4 wave activity seen at geosynchronous orbit with simultaneous gr ound Pc 3-4 pulsations at auroral latitudes. We found that at geosynch ronous orbit the majority of coherent Pc 3-4 events were azimuthally o r radially polarized. A number of transverse events revealed clear fie ld line resonance (FLR) signatures in the latitudinal power, polarizat ion, and phase variations. However, the FLR characteristics often appe ared to be masked by ionospheric screening and/or wave propagation eff ects. The azimuthal phase propagation was found to be antisunward for most events, although sunward phase propagation has also been observed . The ground Pc 3-4 occurrence, polarization, and longitudinal phase c haracteristics associated with transverse waves were found to be simil ar to those of auroral latitude Pc 5 pulsations. These similarities be tween transverse Pc 3-4 and auroral latitude Pc 5 characteristics may point to a common source mechanism for these pulsations. One event app eared consistent with the excitation of multiple waveguide modes. Most compressional Pc 3-4 activity appeared to be relatively broadband and virtually unpolarized. However, the center frequency of the dominant band was found to be well correlated with the interplanetary magnetic field magnitude. Power spectra from the ground stations usually contai ned significant signal power within the frequency band of the compress ional perturbation seen by GOES 7. It is shown that at some frequencie s, the broadband compressional waves may excite local held line resona nces, whereas at other frequencies the compressional signal is transmi tted to the ground without obvious resonance structures. The ground Pc 3-4 occurrence, spectral, polarization, and longitudinal phase charac teristics associated with compressional waves were found to differ in several respects from the signal characteristics associated with trans verse waves: These differences between transverse and compressional Pc 3-4 waves argue against upstream waves being the sole source of auror al latitude Pc 3-4 pulsations.