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U. A Dyudina, A. P. Ingersoll, G. E. Danielson (Caltech), R. A. West, K. H. Baines (JPL), Galileo NIMS Team, SSI Team
We present maps of Jovian cloud properties derived from images taken simultaneously by the Galileo Solid State Imaging system (SSI) and the Near Infrared Mapping Spectrometer (NIMS) at visible and near infrared wavelengths, 0.41 to 5.2 microns. Regions containing the Great Red Spot (GRS) and one of the White Ovals were studied. The cloud properties are derived using a radiative transfer model and principal component analysis (PCA) on the image data. The mean spectrum for each region was subtracted from individual spectra taken at each point and the resulting deviations were studied using PCA. The deviation spectra are highly correlated. For example, only three spectral functions (principal components) are needed to describe 92% of the variations. Our results suggest that clouds inside GRS contain violet absorber while White Oval do not have it, even though the regions are similar in other wavelengths. We used a radiative transfer model to determine what variations in the cloud structure correspond to the principal components. Our model is based on the cloud structure that accounts for the spectrum of GRS averaged over the region derived in Banfield et al. (1998). Based on the modeling, the first principal component indicates a simultaneous increase in the optical depth and elevation of the optically thick cloud near the NH3 condensation level (approximately 0.6 bar) within both the GRS and White Oval. The difference between principal components 2 and 1 is interpreted as the variation in single scattering albedo of the diffuse cloud layer occupying the 0.2 - 0.6 bar level. The corresponding map suggests a narrow ring of dark haze surrounding the GRS and White Oval at these altitudes. Another possibility is that the difference PC2 - PC1 represents a variation in optical thickness of the cloud at 0.6 bar, but the fit is not as good.
Banfield, D. J.,et al., Jupiter Cloud Structure from Galileo Imaging Data, Icarus, in press, 1998
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