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C.A. Griffith (University of Arizona), C.P. McKay (NASA Ames Research Center)
Recent images of Titan reveal clouds at high southern latitudes (Roe et al. 2002, Brown et al. 2002), which reside in Titan's mid-troposphere and vary dramatically over hour time scales. Griffith et al. (2000) hypothesize that Titan possesses methane condensation clouds that evolve convectively, because their altitudes are consistent with the final resting place of convectively buoyant parcels. Yet, Titan's equatorial thermal profiles at equinox, measured at sunrise and sunset by Voyager, were found to be stable to convection for subsaturated conditions (McKay et al. 1989). The temperature profiles indicate that a surface parcel must be mechanically raised roughly 6 kilometers before achieving buoyancy, assuming 60% humidity. Titan's stability combined with the similarity of the sunrise and sunset profiles above 3 kilometers suggest that the atmosphere was not highly convective at the time and place of the Voyager measurements. Brown et al. (2002) note however that clouds are found at latitudes where the solar insolation exceeds that at the equator during equinox, suggesting that ground heating might instigate convection under these sunny conditions. Here we examine the sensitivity of Titan's thermal profile to seasonal radiative forcing in order to investigate the formation of Titan's clouds and the stability of Titan's atmosphere to convection.
Supported by NASA's Planetary Astronomy Program.
C.A. Griffith, J.H. Hall, T.R. Geballe, Science, 290, 509 (2000)
C.P. McKay, J.B. Pollack, R. Courtin, Icarus, 80, 23, (1989)
M.E. Brown, A.H. Bouchez, C.A. Griffith, Nature, 420, 795, (2002)
H.G. Roe, I. dePater, B.A. Macintosh, C.P. McKay Astrophys. J., 581, 1399 (2002)
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.