UARS OBSERVATIONS OF BIRKELAND CURRENTS AND JOULE HEATING RATES FOR THE NOVEMBER 4, 1993, STORM

Magnetic field and particle observations from the Upper Atmosphere Res earch Satellite particle environment monitor (UARS/PEM) are used to es timate field-aligned currents, electron precipitation energy flux, ion ospheric conductivities, and Joule heating rates during the main phase of the November 4, 1993, geomagnetic storm. From 0300 to 1200 UT on N ovember 4 the auroral oval expanded equatorward of 65 degrees magnetic latitude (MLAT), and UARS encountered the polar cap on seven consecut ive passes during the storm main phase. These passes provide data appr opriate to determine field-aligned currents and estimate ionospheric J oule heating. For this storm, UARS sampled the midnight to dawn sector in the northern hemisphere and the noon to dusk sector in the souther n hemisphere. The maximum net currents on the dayside and nightside ar e comparable and reach 1 A/m for several hours. The average Joule heat ing rates are comparable at midnight, early morning, and noon, where t hey are 9.2, 6.6, and 7.7 GW/h, respectively, but have a strong peak i n the late afternoon, where they are 25.6 GW/h. In contrast, the elect ron precipitation energy deposition is highest near midnight at 5.6 GW /h but drops to less than half this level to 2.4 GW/h and 1.9 GW/h in the early morning and at dusk, respectively, but is very small near no on, only 0.24 GW/h. The Joule to particle energy deposition rate ratio thus varies by roughly an order of magnitude with local time, being o ver 40 near noon, about 20 at dusk, 3 near dawn, and 2 at midnight. Th e hemispherical Joule and electron precipitation heating rates, H-J an d H-elec, are estimated to have been 290 GW and 50 GW, respectively, g iving H-J/H-elec = 4.5 and H-J + H-elec = 340 GW. Differences between these averages and assimilative mapping of ionospheric dynamics (AMIE) results, H-J = 200 GW and H-elec = 80 GW, reflect time variability du ring the storm and are largely resolved when AMIE results only at the times of UARS passes are considered.