SPACE WEATHER - RESPONSE OF LARGE-SCALE GEOPOTENTIALS TO AN INTERPLANETARY MAGNETIC CLOUD

The interaction of solar wind disturbances with the Earth's magnetosph ere can produce disturbances, and at times complete disruptions, of te chnological systems on the Earth and in the space around the Earth. Th is brief report shows the changes induced in the large-scale geopotent ials of the Earth (as provided from measurements across transoceanic c ables) produced by a well-documented interplanetary magnetic cloud eve nt. The study of such a well-measured event can be used to begin to ma ke empirical space weather phenomena more quantitative. We show that g eopotentials at low geomagnetic latitudes can be used to infer the tim e derivative of the near-equatorial magnetic disturbance index, Dst. A t low geomagnetic latitudes, a peak geopotential of about 4 mV/km is f ound 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-equat orial geopotential are linearly related to the energy input to the mag netosphere from the solar wind as given by the epsilon parameter [e.g. , Akasofu, 1979]. We find that an increase in the geopotential of abou t 4 mV/km corresponds to an energy input of about 2.8 x 10(11) W for t he event analyzed here.