The interaction of solar wind disturbances with the Earth's magnetosphere can produce disturbances, and at times complete disruptions, of technological systems on the Earth and in the space around the Earth. This brief report shows the changes induced in the large-scale geopotentials of the Earth (as provided from measurements across transoceanic cables) produced by a well-documented interplanetary magnetic cloud event. The study of such a well-measured event can be used to begin to make empirical space weather phenomena more quantitative. We show that geopotentials at low geomagnetic latitudes can be used to infer the time derivative of the near-equatorial magnetic disturbance index, Dst. At low geomagnetic latitudes, a peak geopotential of about 4 mV/km is found to correspond to a time rate of change of this index of about 50 nT/hr. Further, we show that in this event increases in the near-equatorial geopotential are linearly related to the energy input to the magnetosphere from the solar wind as given by the ε parameter [e.g., Akasofu, 1979]. We find that an increase in the geopotential of about 4 mV/km corresponds to an energy input of about 2.8 × 1011 W for the event analyzed here.