Investigations of Titan's troposphere and surface and Jupiter's great red spot with infrared observations

This dissertation consists of two separate analyses. They pertain to Titan's lower atmosphere and surface, and the visible region of Jupiter's great red spot (GRS).

The large CH$\sb4$ column abundance and haze opacity of Titan's atmosphere prevent observations of Titan's surface in the visible and infrared wavelengths. Constraints on Titan's haze and cloud optical depths, and surface albedo are determined from an analysis of Titan's near-infrared spectrum. Observations of Titan made at the NASA Infrared Telescope Facility (IRTF) are analyzed using a radiative transfer calculation. The depth in Titan's atmosphere penetrated by near-IR solar radiation depends on the strength of CH$\sb4$ absorption, which varies considerably with wavelength. This allows us to separate the effects resulting from haze, clouds and the surface albedo, since these components reside at different atmospheric levels. The results suggest that CH$\sb4$ clouds exist; however they are optically thin or patchy and allow solar radiation to penetrate to the surface. The most plausible interpretation of Titan's albedo at 7700, 6250 and 4900 cm$\sp{-1}$ suggests a surface dominated by "dirty" water ice.

To investigate the chemistry and dynamics of Jupiter's great red spot (GRS), the tropospheric abundances of NH$\sb3$ and PH$\sb3$ in the GRS are determined and compared to those of the surrounding region, the South Tropical Zone (STZ). These gases are possible sources of chromophores, and their distributions are sensitive to the rate of vertical transport in the upper troposphere and lower stratosphere. Three groups of Voyager IRIS spectra are analyzed, two of the STZ and one of the GRS. The two groups of STZ spectra are defined on the basis of their radiances. Variations in the abundances of NH$\sb3$ and PH$\sb3$ are determined within the STZ, as a background for our studies of the GRS. Within the uncertainty of our measurements the PH$\sb3$ mixing ratio at 600 mbar is 3 $\times$ 10$\sp{-7}$, the same for all three selections. The NH$\sb3$ mixing ratio profile in the pressure region between 300 and 600 mbar is the same for both STZ selections. In the GRS, however, NH$\sb3$ is significantly depleted at 300 mbar, with an abundance of 25% that derived for the STZ selections. (Abstract shortened with permission of author.)