The fully developed superrotation simulated by a general circulation model of a Venus-like atmosphere

Formation and maintenance of the fully developed superrotation in the Venus atmosphere are investigated by using a Center for Climate System Research/National Institute for Environmental Study (CCSR/NIES) Venuslike atmospheric general circulation model. Under the condition that zonally uniform solar heating is used, the meridional circulation is dominated by a single cell in a whole atmosphere, and the superrotation with velocities faster than 100 m s^-1 is formed near 60-km altitude. The meridional circulation effectively pumps up angular momentum from the lower to the middle atmosphere. Then the angular momentum is transported by poleward flows of the meridional circulation, and a part of the transported momentum is returned back to the low-latitudinal regions by waves. As a result, the simulated superrotation is formed by the Gierasch mechanism. Equatorward angular momentum flux required in the Gierasch mechanism is caused by not only barotropic waves but also various waves. Rossby, mixed Rossby-gravity, and gravity waves transport the angular momentum equatorward. Although vertically propagating gravity waves decelerate the superrotation above 70 km, the fully developed superrotation can be maintained in the cloud layer (45-70 km).