GROUND OBSERVATIONS AND POSSIBLE SOURCE REGIONS OF 2 TYPES OF PC-1-2 MICROPULSATIONS AT VERY HIGH-LATITUDES

We have used 1-year's data from the recently installed Magnetometer Ar ray for Cusp and Cleft Studies (MACCS) in Arctic Canada and from two s tations of the developing ''conjugate'' array of Automated Geophysical Observatories (AGOs) in Antarctica to study ULF waves in the Pc 1-2 ( 100-600 mHz) frequency band at cusp and polar cap latitudes (Lambda si milar to 74 degrees - 80 degrees), In this paper we focus on the spect ral properties and latitudinal and local time distributions of Pc 1-2 events observed during 1994 and use these along with several case stud ies to infer the source locations of the two major wave types we have observed. We found little variation in center-band frequency of the Pc 1-2 waves we observed, but the average event bandwidth was distinctly wider at stations near 80 degrees MLAT than at stations near 75 degre es MLAT, Broadband waves, with diffuse spectral character, dominated a t the higher latitudes, but their occurrence was confined at most stat ions to within 4 hours of local magnetic noon, Waves with narrower ban dwidth were much more common in our data set, and were the statistical ly dominant wave type at the lower-latitude MACCS stations, Their occu rrence was also limited to the dayside but extended both later and mor e widely in local time than the more broadband waves, These multistati on observations, combined with data from the DMSP, IMP 8, and Geotail satellites, suggest the possibility that these two wave types originat e in quite different regions near the magnetospheric boundary; the mor e narrowband waves in the subsolar and postnoon equatorial region, and the more broadband waves in the high-latitude plasma mantle (and poss ibly at the poleward edge of the cusp), The cusp itself appears to not be a significant source of Pc 1-2 wave activity that can be detected by ground observatories.