Jovian ultraviolet auroral activity, 1981–1991

Abstract

The distribution of auroral brightness on Jupiter's surface as a function of magnetic longitude (System III, 1965) is studied using International Ultraviolet Explorer (IUE) observations of H 2 ultraviolet emissions over the years 1981 to 1991. The brightness is diagnostic of energy input to the atmosphere and of magnetospheric processes. The brightness distribution is determined by assuming model distributions, simulating the observations, and then comparing the predicted vs empirical brightnesses. The model brightness distributions consist of a single peak on top of a baseline emission, constrained to a set of candidate auroral ovals. The north auroral data are best fit by brightness distributions on the oval mapped by the Voyager UVS experiment, compared with footprints of magnetic field lines at L = 5.9, 8, 10, 12, and the last closed field lines. The southern auroral data weakly favor distributions using the L = 8 oval, but all the candidates for the southern ovals fit the observations adequately and produce similar brightness distributions, a consequence of the observational geometry and the limited angular resolution of the IUE instrument. The north and south aurorae appear to be correlated in brightness and in variations of the longitude of peak brightness. The north and south auroral brightness peaks are at ∼194° and ∼24° respectively on average with significant variability about these positions. The average auroral input power to both poles together is (8.2 ± 3.2) × 10 13 W (heavy ion primaries) or (4.3 ± 1.5) × 10 13 W (electron primaries). No long-term trend in the auroral brightness or morphology is detected between solar minimum and solar maximum, but there are strong fluctuations in all the parameters of the brightness distribution on much shorter time scales.