U.A. Dyudina, G.E. Danielson, R.A. West, A. P. Ingersoll,
K.H. Baines and the Galileo NIMS and SSI teams.
Dep. of Geological and Planetary Sci., JPL, Caltech
,Pasadena,CA

"Clouds near Great Red Spot and White Oval. Spectral
classification and interpretation of Galileo images in 26
wavelengths"

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 $\mu$m. 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. So only a few
independent spectral functions (principal components) are
needed to describe most of the deviations. According to
this correlation and using first 3 principal components we
spectrally classify different areas of the GRS and White
Oval. We show this classification on the false color map
which in 3 colors represents 92\% of correlated brightness
variations in 26 wavelengths.
We used a radiative transfer model to determine what
variation in the cloud structure correspond to the
principal components. Based on this 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. The result is
consistent with an updraft in the center of the GRS and
the White Oval and a downdraft in the surrounding rings.