Physics
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........30h&link_type=abstract
PhD Dissertation, Georgia Inst. of Tech. Atlanta, GA United States
Physics
Aerosols, Albedo, Haze, Reflectance, Titan, Satellite Atmospheres, Atmospheric Circulation, Atmospheric Models, Two Dimensional Models, Wind Velocity, Sky Brightness
Scientific paper
At 0.47 microns and 0.55 microns, the geometric albedo of Titan has been observed to vary over the past two decades. Variations in atmospheric reflectance are used to explain these observations, and are postulated to be determined by the haze layer in the atmosphere, because the haze layer has a global extent and is optically thick in the visible. Therefore, variations in the haze layer are believed to cause the observed variations in the geometric albedo. Two controls on the haze layer are examined for the source of the observed variations. Each examination consists of two parts: time simulations of the haze layer, and comparisons between the predicted reflectances and the observations. The first part simulates the haze layer by using an aerosol model. The comparison test is accomplished by radiative transfer calculations of the results from haze simulations. Production of the haze layer is one control on the haze layer and is examined with an aerosol model which has been applied to Titan. The circulation of the atmosphere is the second control which produces the haze variations. The control from the circulation is examined by an aerosol model which is two dimensional. A two-dimensional model is constructed to accomplish the second examination, because the existing model is inadequate. A wind field is derived to represent the circulation in the atmosphere and induces variation in the haze layer. The circulation of the atmosphere is determined to be a better source of the observations of the geometric albedo and the hemispheric brightness for two reasons. The variations in the production rate produced only the size of the observed variations. The variations in the circulation matched the size and the temporal variations of the observations. The circulation source was also considered the better source of the observed variation, because the observations were not reproduced by using model parameters which may be physically implausible. The conclusion on the source for the observations does have reservations. Problems were indicated, because our simulations of the hemispheric brightness contrast were poor. The representation of the circulation is most likely the cause of this failure. Our representation of the circulation was an extreme simplification of the actual circulation, because derived wind field was one large cell for the entire stratosphere and did not include small scale processes. The wind field for the haze model also derived with several assumptions which are probably not true for Titan.
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