JUPITERS CLOUD STRUCTURE FROM GALILEO IMAGING DATA

The vertical structure of aerosols on Jupiter is inferred from data ob tained by the NASA Galileo Solid State Imaging system during the first six orbits of the spacecraft. Images at 889 nm (a strong methane band ), 727 nm (a weaker methane band), and 756 nn (continuum) taken at a v ariety of lighting and viewing angles are used. The images are display ed and described in the companion paper by Vasavada et al. (1998, Icar us 135, 265-275). Conservative scattering cloud particles with lateral ly uniform single scattering properties are assumed in the analysis an d are shown to be consistent with the data at these wavelengths. Parti cles are bright, and the darkest locations on Jupiter correspond to th e smallest optical thickness of aerosols, Optical depths and vertical positions of aerosol layers vary from place to place and are the retri eved quantities in the analysis. Only mid and low latitudes are sample d in this data set. A stratospheric haze with an optical depth of roug hly a tenth and an upper tropospheric haze with an optical depth of 2 to 6 exist over all regions. Both are consistent with previous conclus ions based on data of lower spatial resolution (e.g., West et al. 1986 , Icarus 65, 161-217). The new data show that these layers contain lit tle lateral structure on scales smaller than the planetary jets. On sc ales of the jets and ovals, the top and bottom of the upper tropospher ic haze vary in elevation. The concentration of particles (optical dep th per pressure interval) varies less than does the total optical dept h. Near the base of the upper tropospheric haze is a third cloud compo nent, usually at pressure p = 750 +/- 200 mb, which is less than a sca le height in geometric thickness. Its optical depth varies from zero t o about 20 on regional scales and often varies by 50% on scales of a f ew tens of kilometers. Optical depth variations in this cloud are the principal cause of the features in Jupiter's atmosphere seen at red an d longer wavelengths. It is probably composed of ammonia. The expected NH4SH cloud has not been identified in this work, perhaps because it exists only at locations where it is concealed beneath higher clouds. Our retrievals also cannot rule out a pervasive deep haze without smal l-scale structure. Finally, in one region northwest of the Great Red S pot, a deeper cloud is identified. Parts of it lie at a pressure great er than four bars. It is associated with a rapidly changing storm syst em with optical depth of several tens (or more) and a range of cloud h eights between p > 4 bars to p similar to 400 mb. It is probably compo sed of water. (C) 1998 Academic Press.