GLOBAL ENERGY DEPOSITION DURING THE JANUARY 1997 MAGNETIC CLOUD EVENT

The passage of an interplanetary magnetic cloud at Earth on January 10 -11, 1997, induced significant geomagnetic disturbances, with a maximu m AE in excess of 2000 nT and a minimum Dst of about -85 nT. We use a comprehensive set of data collected from space-borne instruments and f rom ground-based facilities to estimate the energy deposition associat ed with the three major magnetospheric sinks during the event. It is f ound that averaged over the 2-day period, the total magnetospheric ene rgy deposition rate is about 400 GW, with 190 GW going into Joule heat ing rate, 120 GW into ring current injection, and 90 GW into auroral p recipitation. By comparison, the average solar wind electromagnetic en ergy transfer rate as represented by the Ε parameter is estima ted to be 460 GW, and the average available solar wind kinetic power U SW is about 11,000 GW. A good linear correlation is found between the AE index and various ionospheric parameters such as the cross-polar-ca p potential drop, hemisphere-integrated Joule heating rate, and hemisp here-integrated auroral precipitation. In the northern hemisphere wher e the data coverage is extensive, the proportionality factor is 0.06 k V/nT between the potential drop and AE, 0.25 GW/nT between Joule heati ng rate and AE, and 0.13 GW/nT between auroral precipitation and AE. H owever, different studies have resulted in different proportionality f actors. One should therefore be cautious when using empirical formulas to estimate the ionospheric energy deposition. There is an evident sa turation of the cross-polar-cap potential drop for large AE(>1000 nT), but further studies are needed to confirm this.