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

Abstract

The effects of sea surface temperature (SST) variations and large‐scale dynamics on the cloud feedback and water vapor feedback are quantified using a fine‐scale numerical model, or cloud‐resolving model, in which the cloud‐scale dynamics is explicitly treated instead of being parameterized as is necessary in a general circulation model. The SST variation has large impacts on the water vapor feedback and small impacts on the cloud feedback, radiation budget, and surface energy budget under a given large‐scale dynamic state. As the SST gets warmer (increasing 2°), the warm and moist equilibrium 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) at the surface due to the increase of surface evaporation is almost compensated 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 slightly affects the equilibrium states of temperature and water vapor mixing ratio; the relative humidity is decreased above 10 km and increased below; and the cloud amount and convective intensity are enhanced. Both the variations of SST and large‐scale dynamics are positively correlated with the surface precipitation.