Hydromagnetic (ULF) Power at Separated Sites (DELTA lambda ~ 90 sup o ) at Mod- to Low-Latitudes.

The power spectra of geomagnetic field fluctuations in the hydromagnetic wave band of periods 20 to 600s have been systematically evaluated from data acquired at L'Aquila, Italy (LAMBDA ~ 42. 5 sup o ; L ~ 1.6) and Green Hill, R.I. (LAMBDA ~ 52 sup o ; L ~ 2.8) during July 1985. The average levels of the ULF power in different frequency bands have been compared. Autocorrelations of power levels for the data at the two stations show a clear 24 hour recurrence period at L'Aquila in the bands 20-30s and 30-45s, while the same periodicity is clearly observed at Green Hill for the 30-45s and 45-150s bands. The cross correlation analyses of the data, organized both as a function of LT and UT, indicate that there is a UT dependence for the two longer period bands, suggesting global source influences on the power levels. The power in the shorter period band appears to be driven by more "local" magnetosphere/ionosphere conditions.