[Previous] | [Session 41P] | [Next]
F. Hourdin (LMD/CNRS, Paris, France), P. Rannou, Michel Cabane (SA/CNRS, Paris, France), C. P. McKay (NASA, Ames), D.q Luz (Observatorio Astronomico de Lisboa, Portugal)
Laboratoire de Météorlogie Dynamique has developed, in collaboration with DESPA (obs. Parid-Meudon) and the NASA Ames Research Center, the first General Circulation Model of the atmosphere of Titan (Hourdin et al., Icarus, Vol 117, p. 358-374, 1995). The model has produced a strong superrotation of the stratosphere with zonal winds above the equator of the order of 100~m/s (about ten times the rotation of Titan's surface) in good agreement with the few observational informations available. The numerical results have aslo reinforced the idea of a strong coupling between atmospheric dynamics, aerosol physics and chemistry on Titan. We are now involved in the development of a fully coupled circulation model including those additional processes. For reasons of numerical cost, this study is conducted with a bi-dimensional latitude-altitude axi-symmetric version of the circulation model. We present results obtained with this axi-symmetric model. The results show time constants for atmospheric transport larger than a season in the troposphere, but much smaller in the stratosphere. However, these time constants are strongly sensitive to the effiency of the transport by transient eddies which must be parametrized in this axi-symmetric model. We also present coupled results in which transport and microphysics of aerosols are accounted for as well as there radiative feedback on atmospheric circulation. Areosols are considered as fractal particules (Rannou et al.,Icarus, Vol 96, p.355-372, 1995). The coupled model is able to reproduce satisfactory well the order of magnitude of the latitudinal and seasonal albedo contrasts observed at the time of Voyager encounter or more recently from ground-based or HST observations.