DPS 35th Meeting, 1-6 September 2003
Session 10. Titan I
Oral, Chairs: C. A. Griffith and D. B. Curtis, Wednesday, September 3, 2003, 10:30am-12:00noon, DeAnza I-II

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[10.02] Entropy and Mixing : Titan's Humidity Revisited

R. D. Lorenz (LPL, University of Arizona)

Determinations of the relative humidity of methane near Titan's surface range from 40-60 %. The rationale advanced by Lunine in the global ocean hypothesis was that a mixed ethane-methane ocean in thermodynamic equilibrium with the atmosphere would be unsaturated due to methane vapor pressure supression by involatile ethane (much as salt or sugar dissolved in water slows its evaporation). Here I explore a nonequilibrium explanation for the incomplete saturation - the reason why the terrestrial atmosphere is not saturated. Specifically, saturated near-surface air is mixed with downwelling dry air, a mixing driven by vertical convection. The more vigorous the mixing, the dryer the near-surface air should be. Flasar (1983) made a crude empirical evaluation of transport processes : here I adopt a more fundamental thermodynamic approach. In reality both the involatile solute and the mixing mechanisms probably play a part in regulating methane humidity, and the utility of global and annual averages must be compromised by latitudinal and seasonal dependences. Comparison with the Earth - where moist processes play a dominant role in the entropy budget - will be instructive.

If you would like more information about this abstract, please follow the link to http://www.lpl.arizona.edu/~rlorenz. This link was provided by the author. When you follow it, you will leave the Web site for this meeting; to return, you should use the Back comand on your browser.

The author(s) of this abstract have provided an email address for comments about the abstract: rlorenz@lpl.arizona.edu

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.