Multiple Equilibrium States Appearing in a Venus-Like Atmospheric General Circulation Model

抄録

We investigated the existence of multiple equilibrium states in the Venusian atmospheric general circulation suggested by Matsuda (1980, 1982) using a Venus-like atmospheric general circulation model. We ran the model from two initial conditions: a state with large zonal wind increasing with height and a motionless state. For the large zonal wind initial state, a strong zonal wind with weak meridional circulation, i.e., super-rotation, appears. However for the motionless initial condition, slow zonal wind with strong meridional circulation relative to the farmer state appears. Each circulation reached a quasi-steady state. These results have the same features suggested by Matsuda. The presence of multiple equilibrium states was sensitive to the horizontal eddy viscosity parameter. For the strong zonal wind state, the acceleration of the zonal mean zonal wind results from the horizontal EP flux divergence from the wavenumber one component on the equator, which is mainly maintained by the Gierasch mechanism (1975). The presence of multiple equilibrium states suggests that an alternative slow zonal wind state could appear in the Venusian atmosphere if an appropriate initial condition or drastic fluctuation is assigned.