Ground observations and possible source regions of two types of Pc 1-2 micropulsations at very high latitudes

We have used 1-year's data from the recently installed Magnetometer Array for Cusp and Cleft Studies (MACCS) in Arctic Canada and from two stations 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 (Λ ∼ 74° – 80°). In this paper we focus on the spectral properties and latitudinal and local time distributions of Pc 1–2 events observed during 1994 and use these along with several case studies 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° MLAT than at stations near 75° MLAT. Broadband waves, with diffuse spectral character, dominated at the higher latitudes, but their occurrence was confined at most stations to within 4 hours of local magnetic noon. Waves with narrower bandwidth were much more common in our data set, and were the statistically dominant wave type at the lower-latitude MACCS stations. Their occurrence was also limited to the dayside but extended both later and more widely in local time than the more broadband waves. These multistation observations, combined with data from the DMSP, IMP 8, and Geotail satellites, suggest the possibility that these two wave types originate in quite different regions near the magnetospheric boundary; the more narrowband waves in the subsolar and postnoon equatorial region, and the more broadband waves in the high-latitude plasma mantle (and possibly 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.

Details