Energy dissipation during a geomagnetic storm: May 1998 Original Research Article

The energy input to the magnetosphere and its dissipation in the inner magnetosphere during a storm on May 2–9, 1998 is discussed. The methods to evaluate the energy input and the energy dissipation into the ionospheric Joule heat and the ring current are reviewed. It is shown that the energy dissipated in the ionosphere during individual substorms is proportional to the energy input during the same period. However, during very large input, the energy dissipation into the ionosphere seems to grow only slowly, and thus there seems to be a limit to how much energy can be dissipated via Joule heating. The ring current energy is evaluated using the Dst index and direct particle measurements. The reasons for the smaller values obtained by direct particle measurements are discussed. In total, it seems that during this very strong storm the ring current energy was only about half of the Joule heat, but the two together are less than a third of the total energy input. It is suggested that most of the energy during very strong driving is lost back to the solar wind.