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A.R. Vasavada, A.P. Ingersoll (Caltech), P.J. Gierasch, D. Banfield, A. Simon-Miller (Cornell), Galileo SSI Team
The Galileo spacecraft's Solid State Imager (SSI) has been returning high-quality mosaics of Jupiter since 1996. The combination of high spatial resolution (30 km/pix), broad spectral range (0.4 to 0.9 microns), and short mosaic time steps (1 hr) has revealed a dynamic, vertically extended cloud structure not detectable by Voyager. Images have been acquired near the center of the sunlit hemisphere, on the planetary limb, at high phase angles, and on the night side, at all latitudes.
Based on a systematic analysis of these data, a new view of Jupiter's global-scale dynamics and energetics has begun to emerge (see Nature 403, pp.628-632, 2000). Our nightside images have shown that jovian lightning, while as active as terrestrial lightning, is restricted to latitude bands where the horizontal shear in the zonal flow is cyclonic. These regions are generally clearer (which presumably indicates downwelling), but also contain chaotic cloud patterns and small, bright outbursts of cloud material. The latter correspond with the locations of lightning storms observed on the night side.
Multispectral analyses of the lightning-bearing bright clouds have shown that their vertical extent ranges from above the visible cloud tops down to levels at which water is the only reasonable condensate. We suggest that these are regions of vigorous moist convection on Jupiter, either vertically distinct from or contained within the Voyager-era model of up/downwelling in the anti/cyclonic regions. Simple calculations show that these storms may transport the bulk of energy from Jupiter's interior. Furthermore, these localized upwellings may form eddies at the visible cloud level which eventually transfer their momentum into the zonal jets, sustaining them.