Jovian auroral ovals inferred from infrared H3(+) images

Detailed analyses have been carried out of infrared H3(+) images of Jupiter's polar regions observed with the ProtoCam camera on the Infrared Telescope Facility (IRTF) on March 3-6, 1992. The images were obtained at 3.5 microns, where H3(+) emission is strong and the jovian disk is dark. By carefully examining the H3(+) emission over the limb of the polar regions, we find that the H3(+) emission extended significantly above Jupiter's limb in the north polar region and to a lesser degree in the south polar region. This could be due to either a highly extended thermosphere or a broad energy spectrum of precipitating particles in the auroral regions. After we applied a new technique to the H3(+) images to remove limb brightening, we found auroral ovals in both polar regions. The northern oval appears to be close to the L = 30 footprint in the magnetospheric spot locations derived from previous analyses. One intrinsically bright area is found in the northern oval approximately at 150 deg longitude (System III) and 70 deg latitude, where the oval is also wider than elsewhere. The intensity of the bright area varies with a time scale as short as 50 min. The southern oval seems to occur at latitudes higer by a few degrees than the L = 30 footprint, although L = 30 is within the uncertainty of latitude determination. One or two localized intensity maxima are found in the southern oval between 0 deg and 70 deg longitude.