Geomagnetic energies are computed at hourly intervals for three period bands (in the Pc 3--5 range) from horizontal component nagnetometer data recorded at Pittsburg, New Hampshire (L~3.5), Girardville, Quebec (L~4.4), and their approximate conjugate location at Siple, Antarctica (L~4.0). The data were recorded during September 23--29, 1977, a relatively quiet to moderately disturbed geomagnetic interval. High correlations are found at all three stations between dayside ground magnetic energies and the solar wind kinetic energy flux density by using multivariate analysis techniques. The interplanetary quantity &egr;, whose values did not exceed 4¿1018 erg/s for this data set, is found not to have a significant association with dayside magnetic activity. The similar results found at the conjugate stations indicate that the solar wind kinetic pressure variations are important to control dayside broadband magnetic fluctuations in the Pc 3--5 frequency range measured on the ground.