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D. Luz (Observatório Astronómico de Lisboa, Portugal), F. Hourdin (Laboratoire de Météorologie Dynamique du CNRS, Paris)
Numerical modeling of Titan by Hourdin et al. (1995, Icarus 117, p. 358) has suggested that the mean zonal circulation at 1 mb may be barotropically unstable in the vicinity of the strong jets that exist at high latitudes. In support of the Gierasch mechanism as a driver for superrotation, their results indicate that large scale barotropic eddies may transport angular momentum equatorward from high latitudes, thereby closing the angular momentum budget.
We have used a 2-dimensional, longitude-latitude model of the shallow-water equations on the sphere to investigate the role of the transient eddies on the transport of trace chemical species. Our results suggest that the eddies are large-scale atmospheric waves and that the transport of trace species is strongly latitude-dependent. Latitudinal mixing is small on the poleward edges of the jets, but strong on the unstable, equatorward edges. The effect of a simple coupling of trace species and dynamics in the model by parameterizing the altitude distribution of a trace species and the seasonal variations of the meridional circulation will be discussed.
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