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K.H. Baines, R.W. Carlson, L.W. Kamp (JPL/CalTech), Galileo/NIMS Team
Since June 1996, Galileo/NIMS has acquired multi-spectral near-infrared (0.73 - 5.2 micron) maps of a number of large-scale anti-cyclonic systems. These include the Great Red Spot, White Ovals BC, DE and the merged "BE" system, and a "Little Red Spot" in the northern hemisphere. Significant variability in aerosol color and single-scattering albedos are found between the high-altitude cores of these features and their surrounding collars of low-opacity, low-level hazes. For example, adopting the red phase function of Tomasko et al (1978; Icarus 33, 558-592), the core of the Great Red Spot (GRS) exhibits high-opacity (>3.0) clouds extending to above the 300 mbar level with single scattering albedos near 0.997, 0.993, and 0.998 at 0.76, 0.95, and 1.6 micron, respectively. In contrast, the surrounding collar of low opacity (<1.00), low-lying (> 500 mbar) hazes are significantly darker, with single-scattering albedos near 0.90, 0.98, 0.96 at these wavelengths.
Cloudy turbulent regions to the northwest of the Great Red Spot (GRS) and between White Ovals BC and DE exhibit large spatial gradients in cloud heights and ammonia column abundances. Reflectivity in the 1.48-micron ammonia band varies by >50% in an anomalous cloud feature in the turbulent wake region (TW) to the northwest of the GRS and by > 300% in the inter-White-Oval region (IWO). This TW feature is relatively bright in methane, hydrogen and NH3 absorption passbands, indicating a relatively high altitude, yet exhibits unusually dark reflectivity at 2.73 micron, corresponding to a single scattering albedo < 0.91 compared to ~ 0.96 for a neighboring cloud; yet both clouds exhibit bright single-scattering albedos (> 0.993) at 0.76, 0.90, and 1.60 microns, comparable to the GRS itself. As suggested in our previous report (Baines et al., 1998, BAAS 22, 1070), this feature may be the result of unusually strong vertical transport of large particle size condensate material induced by the GRS's strong wake dynamics.