Multi-spectral imagery of Jupiter's Great Red Spot (GRS) acquired over three jovian rotations by the Galileo/NIMS are used to constrain the vertical aerosol structure and the windfield in and around this most- prominent of anti-cyclonic features. A wide range of atmospheric absorption strengths are covered by the 23 selected NIMS bandpasses, - which include weak, medium, and strong methane and hydrogen absorptions at 0.734, 0.898, 1.761, 2.042, 2.094, 2.168, and 2.375 mu m - allowing NIMS to isolate in altitude prominent aspects of the GRS. The apparent size of the GRS varies markedly with bandpass, its linear dimensions shrinking to about 3/4 its visual size in moderate absorption wavelengths, indicating a bulk elliptical-"wedding cake" shape in its overall three-dimensional cloud structure. The GRS disappears at 2.375 mu m, the strongest absorption bandpass, showing that the GRS is tropospheric. Along the eastern edge, a bright "leading edge"feature is observed on all three rotations, most prominent in all continuum bandpasses from 0.759 to 2.73 mu m, indicative of a relatively low-lying yet optically-thick cloud. Its persistence is suggestive of formation by orographic uplift. The most-prominent continuum feature lies 4.5deg to the west of the eastern edge, about midway to the center of the GRS. Preliminary analysis of this feature - utilizing a 2-cloud model with a particle-to-gas scale height of unity within the uppermost ammonia cloud - indicates a cloudtop near 260 mbar, and opacities of ~ 5.4 and 0.51 at 0.8 and 2.1 mu m, respectively, corresponding to a mean particle size for Mie scatterers of 0.375 mu m and an ammonia mass column density of ~ 70 mu gm/cm(2) . With the same aerosol number density, the cloudtop of the "leading edge" feature is ~ 60 mbars ( ~ 3 km) deeper. Just outside the GRS, the same model yields a cloudtop ~ 3 km deeper still, i.e., near 380 mbar.
AAS/Division for Planetary Sciences Meeting Abstracts #28
- Pub Date:
- September 1996