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E. L. Barth, O. B. Toon, L. W. Esposito (Laboratory for Atmospheric and Space Physics, U. of Colorado, Boulder), E. F. Young (Southwest Research Institute)
Toon et al. (1992, Icarus 95, 24-53) constrained Titan's aerosol distribution for the first 600 km of the atmosphere using a microphysics model. They found that that particles with size on the order of 0.1 \mum and a strongly wavelength dependent optical depth with a value at 1 \mum near 0.5, were consistent with currently available observations.
We have revised the model to include a high altitude ethane vapor flux (5.8 molecules/cm2/s) which leads to the formation of clouds in the lower stratosphere and troposphere. The cloud particles tend to be larger than the aerosol particles, but much less abundant due to large, assumed, nucleation barriers. Nucleation occurs mostly at 52 - 54 km altitude. The particles produced are sparse and grow to 100's of microns and so do not have a significant visible optical depth. Some transient nucleation events below 20 km could allow clouds to be visible for short periods of time. Optical depths are calculated at near-infrared wavelengths for comparison with HST WFPC2 images.
This work was supported by NASA grant NAG5-6900.