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E. L. Barth, O. B. Toon (LASP,University of Colorado)
Microphysical modeling has shown that Titan's atmosphere can sustain clouds composed of ethane ice particles throughout much of the troposphere and lower stratosphere. The nature of these clouds is controlled by various factors for which very little data is known. These factors include the mixing time in the troposphere, the critical saturation ratio for ethane ice, the existence of a surface reservoir of ethane, the magnitude and timing of dynamically driven temperature perturbations, and the abundance and life cycle of methane clouds. We have explored various scenarios and will report on the results. Most noteably, if ethane clouds can form at relatively low supersaturations (~0.15), they have a lifetime of about 20 days. The optical depth of the ethane clouds near the surface could reach that of tholin in the near-infrared, resulting in a 5% increase in Titan's albedo for wavelengths between 1 and 2 microns. Though the optical depth of ethane clouds near the tropopause is typically low, short-lived clouds with optical depths of order 0.1 - 1 can be created sporadically by dynamically driven atmospheric cooling. The addition of methane clouds significantly changes the lifetime of the ethane clouds. Should significant ethane clouds be observed by the Cassini spacecraft, it would indicate either a very lucky chance encounter, or that Titan's atmosphere is dynamically much more active than is currently thought.
This work was funded through JPL 961196 and the Planetary Atmospheres Program, Grant NAG5-6900.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.