Effects of sea surface temperature and large-scale dynamics an the thermodynamic equilibrium state and convection over the tropical western Pacific

The effects of sea surface temperature (SST) variations and large-scale dyn amics on the cloud feedback and water vapor feedback are quantified using a fine-scale numerical model, or cloud-resolving model, in which the cloud-s cale dynamics is explicitly treated instead of being parameterized as is ne cessary in a general circulation model. The SST variation has large impacts on the water vapor feedback and small impacts on the cloud feedback, radia tion budget, and surface energy budget under a given large-scale dynamic st ate. As the SST gets warmer (increasing 2 degrees), the warm and moist equi librium state of temperature and water vapor mixing ratio is obtained; the upper tropospheric relative humidity is enhanced; and the cloud amount and convective intensity are slightly reduced. The cooling (about 10 W m(-2)) a t the surface due to the increase of surface evaporation is almost compensa ted by the warming at the surface due to the increase of surface shortwave flux, which results in a small increase of net surface heat flux. However, the change of large-scale dynamics has large effects on the cloud feedback, radiation budget, and surface energy budget and small effects on the water vapor feedback under a constant SST. An increased large-scale forcing slig htly affects the equilibrium states of temperature and water vapor mixing r atio; the relative humidity is decreased above 10 km and increased below; a nd the cloud amount and convective intensity are enhanced. Both the variati ons of SST and large-scale dynamics are positively correlated with the surf ace precipitation.