37th DPS Meeting, 4-9 September 2005
Session 45 Titan's Atmosphere
Poster, Wednesday, September 7, 2005, 6:00-7:15pm, Music Recital Room

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[45.07] Seasonal variations of Titan's stratospheric composition in the LMD/SA Global Climate Model

A. Crespin, S. Lebonnois, F. Hourdin (LMD/IPSL, Paris, France), P. Rannou (SA/IPSL, Verrieres, France)

The CIRS/Cassini observations of Titan's stratosphere are providing new data on its composition, at a different season from Voyager. Together with some data available from ground-based observations, these data now provide informations on the seasonal evolution of Titan's stratospheric composition. Among the observed seasonal variations, one big question is the change in the altitude of the detached haze layer (which is associated with the haze production zone in our current understanding of the haze distributions, Rannou et al. 2002), from roughly 350 km at the Voyager epoch to approximately 500 km now.

The 2-dimensional LMD/SA Global Climate Model includes a photochemical module, and calculates the atmospheric composition (44 species) in the range 0-500 km of altitude, given boundary fluxes at the top (since many constituants are mainly produced above that altitude). We present here the stratospheric composition obtained in our simulations, compared to the available observational dataset. Evolution of the observed stratospheric distributions between Voyager and Cassini is compared to the seasonal evolution predicted by the model. Cassini also provides some vertical profiles of given compounds (CIRS limb observations), which we can interpret using our modeled distributions. We also discuss the sensitivity of the retrieved seasonal and latitudinal behaviour to several parameters: boundary conditions, UV actinic fluxes, altitude of the haze production zone.

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Bulletin of the American Astronomical Society, 37 #3
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