SST Variability and its Mechanism in a Coupled Atmosphere/Mixed-Layer Ocean Model
Akio Kitoh, Tatsuo Motoi and Hiroshi Koide
Meteorological Research Institute
To give some insight for mechanisms on air-sea interaction with interannual and interdecadal time scale, SST variability in a coupled atmosphere/mixed-layer ocean model is investigated. The model has no ocean dynamics, but shows a large SST variability in the tropical Pacific with a time scale of about 10 years. The basin-scale feature of SST variation has some common characteristics shared with that obtained by a global ocean/atmosphere coupled GCM and observational data in the subtropical to the mid-latitude Pacific. Both the latent heat flux and shortwave radiation have their roles in producing the tropical SST anomalies. There is no large contrast in the total heat flux between the eastern and the western Pacific. However, their main components, the shortwave radiation and the latent heat flux, have a remarkable contrast between the cold tongue in the east and the warm pool region in the west. In the east, the ocean is warmed by- shortwave and cooled by latent heat. This shortwave radiation is negatively correlated with low level clouds. When the SST is warmer than normal in the eastern Pacific, there is less low level stratus clouds and more shortwave radiation reaching the surface. In the western Pacific, the ocean is warmed by less evaporation due to weaker winds. When the ocean becomes warm, it is cooled by less shortwave radiation due to stronger activity in cumulus convection.