Abstract. Beginning from the hypothesis by Bjerknes [1969] that oceanatmosphere interaction was essential to the E1 Nifio-Southern Oscillation (ENSO) phenomenon, the Tropical Ocean-Global Atmosphere (TOGA) decade has not only confirmed this but has supplied detailed theory for mechanisms setting the underlying period and possible mechanisms responsible for the irregularity of ENSO. Essentials of the theory of ocean dynamical adjustment are reviewed from an ENSO perspective. Approaches to simple atmospheric modeling greatly aided development of theory for ENSO atmospheric feedbacks but are critically reviewed for current stumbling blocks for applications beyond ENSO. ENSO theory has benefitted from an unusually complete hierarchy of coupled models of various levels of complexity. Most of the progress during the ENSO decade came from models of intermediate complexity, which are sufficiently detailed to compare to observations and to use in prediction but are less complex than coupled general circulation models. ENSO theory in simple models lagged behind ENSO simulation in intermediate models but has provided a useful role in uniting seemingly diverse viewpoints. The process of boiling ENSO theory down to a single consensus model of all aspects of the phenomenon is still a rapidly progressing area, and theoretical limits to ENSO predictability are still in debate, but a thorough foundation for the discussion has been established in the TOGA decade.

No abstract

No abstract

969 IntroductionVenus has a thick CO 2 atmosphere with surface pressure of 9.2 × 10 4 hPa. The surface temperature is about 730 K because of the greenhouse effect imparted by thick CO 2 gas. Sulfuric acid clouds blanket the entire planet at about 47−70 km. An important characteristic of Venus is its very slow rotation: its rotation period is 243 earth days. One Venus Solar day is 117 days considering both daily rotation and revolution. It might therefore be speculated that convection between dayside and nightside dominates the atmospheric circulation, and that the convection pattern moves slowly together with slowly migrating subsolar and antisolar points. However, such a convection has not been observed, and observations have confirmed that fast zonal winds, called super-rotation or four-day circulation, are predominant. The Venusian cloud pattern rotates in the same direction as the rotation of the solid Venus with about four days around Venus along the equator. The zonal wind speed increases with height; its velocity is about 100 m s −1 at the cloud top level (about 70 km). The wind is 60 times faster than the solid planet. The reason why dayside-nightside circulation does not appear but super-rotation (four-day circulation) is dominant remains still unclear. Furthermore, the mechanism producing and maintaining such a fast zonal wind Japan, Vol. 86, No. 6, pp. 969−979, 2008 Journal of the Meteorological Society of AbstractWe investigated the existence of multiple equilibrium states in the Venusian atmospheric general circulation suggested by Matsuda (1980Matsuda ( , 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.

No abstract