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D. Banfield, P. J. Gierasch (Cornell), A. P. Ingersoll, A. R. Vasavada (Caltech)
We present a method for identifying and determining altitude constraints on deep (below the ammonia cloud deck) clouds on Jupiter, using Galileo SSI images. The fundamental concept is that contrasts on small spatial scales ( ~30 km) show different amplitudes in a continuum filter relative to contrasts in a methane absorption band filter (Banfield et al., Icarus, 1998). The ratio of the amplitide variations gives a measure of the methane path length and thus of the depth, if scattering properties of overlying clouds are known.
A difficulty is that the ammonia cloud sheet is almost ubiquitous on Jupiter and of moderate optical depth. Thus, in most locations, contrast in the ammonia clouds obscures contrasts due to deeper clouds. In locations where the ammonia cloud is thin and featureless, constraints can be placed on the altitude of deeper clouds. In other locations, the local variations in the two filters can only suggest that there may be more than one level of cloud in addition to the ammonia cloud.
We have identified many regions where clouds exist at depths exceeding 1 bar, and a few locations where clouds exist at pressures exceeding 4 bars (specifically, near convective towers). The deepest are likely to be water clouds, while the more shallow could either be water, NH4SH or perhaps even multiple ammonia layers.