DPS 34th Meeting, October 2002
Session 34. Titan
Poster, Chair(s): , Thursday, October 10, 2002, 4:00-6:30pm, Exhibit Hall

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[34.01] Impact of the Seasonal Variations of Composition on the Temperature Field of Titan's Stratosphere

S. Lebonnois, F. Hourdin (LMD, Jussieu, France), P. Rannou (SA, Jussieu, France), D. Luz (LESIA, Meudon, France), D. Toublanc (CESR, Toulouse, France)

An enrichment has been observed for several compounds in Titan's stratosphere by IRIS/Voyager 1, for high latitudes coming out of winter (Coustenis and Bézard, Icarus 115, 1995). Bézard {\em et al.} (Icarus 113, 1995) suspected that this enrichment could affect the temperature field in Titan's stratosphere by inducing a relative cooling at those latitudes.

The impact of meridional dynamics on the composition of Titan's atmosphere has been studied recently with a 2-dimensional photochemical model (Lebonnois {\em et al.}, Icarus 152, 2001). To go further into the study of the coupling between photochemistry and dynamics, a photochemical module has been directly included into the general circulation model of the Laboratoire de Météorologie Dynamique (described in Hourdin {\em et al.}, Icarus 117, 1995). A simplified module has also been implemented, that uses for a limited number of species a simple linear relaxation toward a prescribed vertical profile, instead of the complex photochemical calculations. This technique, presented in Lebonnois {\em et al.} (2001), allows to reproduce the latitudinal variations observed in the stratosphere of Titan for some species. We consider here the case of C2H2, C2H6 and HCN, which distributions are taken into account in the radiative calculations of the GCM. The contributions of other trace compounds have been neglected.

Using this simplified coupled model, we have studied the impact on the temperature field of the variations of the distributions of C2H2, C2H6 and HCN induced by meridional dynamics. The enrichment obtained in the descending branch of the Hadley cell is associated with a relative cooling around the 0.1 mbar level. Lower in the stratosphere (around 1 mbar), the effect is a slight heating.

We will present these effects and their interpretation, and will discuss their significance, especially when compared to the thermal effects of the coupling between dynamics and the aerosols' distribution.

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