31st Annual Meeting of the DPS, October 1999
Session 41. Titan: Physics
Contributed Oral Parallel Session, Thursday, October 14, 1999, 8:30-9:50am, Sala Pietro d'Abano

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[41.08] Latitudinal Variations in Titan's Atmospheric Composition with a 2D Photochemical Model

S. Lebonnois, D. Toublanc (CESR/CNRS), F. Hourdin (LMD/CNRS)

From IRIS/VoyagerI observations of Titan, Coustenis & Bezard (Icarus 115, 1995) have retrieved the composition of the low stratosphere as function of latitude. The variations observed seem to be a seasonal effect, but are not yet understood. We have investigated the role of the dynamical transport on the latitudinal behaviour of Titan's atmospheric compounds with a 2-dimensional (altitude-latitude) photochemical model. The photochemistry is updated from Toublanc et al (Icarus 113, 1995), the description of the UV flux in the whole atmosphere is done with a 3D Monte-Carlo code in order to be more realistic for all latitudinal and seasonal conditions (Lebonnois & Toublanc, accepted in JGR-Planets, 1999), and we use synthetic meridional winds based on the GCM by Hourdin {\em et al.} (Icarus 117, 1995). The introduction of meridional transport by winds in the stratosphere and mesosphere enables the model to reproduce most of the latitudinal tendencies observed by Voyager in the low stratosphere: the enhancement of HCN from 50\circ~S to 70\circ~N, the stability of C2H6, C3H8 and C2H2 (with its moderate enhancement in the northern high latitudes). In these latitudes, the model yields an enhancement for the other observed species (C2H4, C4H2, C3H4 and HC3N), but not as high as the observed factors ( 70\circ~N/equator~~~10 ). We have also investigated the sensitivity of the stratospheric composition to the dynamical parameters used (eddy diffusion, strength and structure of the winds).

This work is supported by the Programme National de Planetologie of the Institut National des Sciences de l'Univers (CNRS).

The author(s) of this abstract have provided an email address for comments about the abstract: slebonno@cesr.fr

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