Energy densities are computed for geomagnetic field fluctuations in the Pc 3--4 range using H component magnetometer data recorded at South Pole station over a three-month period from June 3 to September 4, 1982. Hourly values of the energy densities in the Pc 3 and Pc 4 period bands are found to be highly correlated during geomagnetic local daytime hours. The results of multivariate analyses between geomagnetic energies and upstream solar wind quantities show that the most important quantity in controlling the magnitude of the field fluctuations is the solar wind speed, with the IMF B2 component being of next importance. We conclude that the Kelvin-Helmholtz instability at the dayside magnetopause is, statistically, the dominant energy source that contributes ot ULF hydromagnetic wave activity at cusp latitudes.