NUMERICAL-SIMULATION OF THE GENERAL-CIRCULATION OF THE ATMOSPHERE OF TITAN

The atmospheric circulation of Titan is investigated with a general ci rculation model. The representation of the large-scale dynamics is bas ed on a grid point model developed and used at Laboratoire de Meteorol ogie Dynamique for climate studies. The code also includes an accurate representation of radiative heating and cooling by molecular gases an d haze as well as a parametrization of the vertical turbulent mixing o f momentum and potential temperature. Long-term simulations of the atm ospheric circulation are presented. Starting from a state of rest, the model spontaneously produces a strong superrotation with prograde equ atorial winds (i.e., in the same sense as the assumed rotation of the solid body) increasing from the surface to reach 100 m sec(-1) near th e 1-mbar pressure level. Those equatorial winds are in very good agree ment with some indirect observations, especially those of the 1989 occ ultation of Star 28-Sgr by Titan. On the other hand, the model simulat es latitudinal temperature contrasts in the stratosphere that are sign ificantly weaker than those observed by Voyager 1 which, we suggest, m ay be partly due to the nonrepresentation of the spatial and temporal variations of the abundances of molecular species and haze. We present diagnostics of the simulated atmospheric circulation underlying the i mportance of the seasonal cycle and a tentative explanation for the cr eation and maintenance of the atmospheric superrotation based on a car eful angular momentum budget. (C) 1995 Academic Press, Inc.