Nighttime thermospheric winds and temperatures over Fritz Peak Observatory (39.9¿N, 105.5¿W) have been determined from the Doppler shifts and line profiles of the (OI) 15876-K (6300 ¿) line emission. The peak winds measured during several geomagnetic storms are shown to be linearly related to the time rate of change of the equatorial ring current parameter (d (DSt)/dt). During these geomagnetic storm periods the time variation of the measured meridional winds are also strongly correlated with the time rate of change of DSt although the observed winds at midlatitudes may lag variations in this parameter by several hours. The energy input that is necessary in a thermospheric dynamic model to bring the calculated meridional winds into agreement with the observations. These results suggest that d (DSt/dt is a useful index for determining the magnitude and time history of the high latitude energy input during both quiet and disturbed geomagnetic conditions for use in global thermospheric dynamic models.