Ogo 5 observations of Pc 5 waves: Ground-magnetosphere correlations

Twenty-two months of Ogo 5 flux gate magnetometer data in the years 1968–1969 have been scanned for the occurrence of Pc 5 waves. Such waves were observed on 18 orbits inside the magnetosphere in the region of L = 6–13 and at a magnetic latitude of 10° to ∼30°. Close correlations between magnetospheric waves and Pc 5 pulsations on the ground were found on 13 orbits. The 15 orbits on which waves were observed in the morning sector of the magnetosphere were between 0300 and 1100 LT. Most Pc 5 waves in the morning were left-hand elliptically polarized with respect to the ambient field. The major axis of the polarization ellipse was directed nearly perpendicular to the ambient field and close to the azimuthal direction. The examination of ground Pc 5 pulsations at a conjugate pair of stations, Great Whale River (GWR) and Byrd (BY), indicates that the Pc 5 wave, in terms of the simple string analogy of field line resonance, is an odd mode. The radial location, local time of occurrence, and polarization of the waves observed in the magnetosphere are in agreement with expectations based on ground observations. The fact that the waves were observed well inside the magnetosphere suggests that if the waves are generated by the Kelvin-Helmholtz instability at the magnetopause, then field line resonances must play a role in establishing the observed wave amplitudes.