Superrotation in a Venus GCM with Realistic Topography and Radiative Forcing

The latest version of the Ashima VenusFMS General Circulation Model (GCM) includes realistic solar and infra-red radiation, topography, and consistent treatment of temperature-dependent heat capacity throughout the GCM. Simulations using this GCM produce significant super-rotating equatorial winds and mid-latitude jets in the upper cloud decks and Sub-Solar to Anti-Solar flow above 90km. Comparison with observations suggests that the GCM is reproducing many of the large-scale features in the middle and upper atmosphere. The local solar time dependence of zonal and meridional winds agrees well with recent ground-based and orbiter observations of the winds. Asymmetric downwelling in the Sub-Solar to Anti-Solar flow above 90km provides a possible explanation for the observed post-midnight maximum in chemical activity involving trace species. Thermal and dynamical features suggest a five layer model of the atmosphere extending from the quiescent boundary layer in the lower atmosphere to the Sub-Solar/Anti-Solar (SS/AS) above 90km. Distinct eddy driven (Ferrel-like) cells and mean overturning (Hadley-like) cells are seen in the time and zonal mean fields, and the observed transition between the Super-rotating middle atmosphere and SS/AS circulation is reproduced. We discuss the results of our latest experiments with this GCM in comparison with observations, and discuss the sensitivity of the simulated circulation to parameterizations involving topography.