Role of surface evaporation in surface rainfall processes
【摘要】：The roles of surface evaporation in tropical surface rainfall processes in rainfall regions (raining stratiform and convective regions) and rainfall-free regions (nonraining stratiform and clear-sky regions) are investigated on the basis of the data from a series of two-dimensional cloud-resolving simulations. The model is integrated for 21 days with imposed zonally uniform vertical velocity, zonal wind, horizontal temperature, and vapor advection, as well as sea surface temperature from the Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE). The model is also integrated to equilibrium states for 40 days with imposed zero vertical velocity, constant zonal wind, and sea surface temperatures of 31°C and 29°C for two separate experiments. The time- and zonal-mean surface evaporation mainly comes from rainfall-free regions, where the surface evaporation is largely balanced by the vapor divergence associated with the subsidence. In rainfall regions the vapor convergence determines the convective rainfall while the surface evaporation plays a negligible role. Thus surface evaporation pumps water vapor into rainfall-free regions, and the divergence transports the vapor from rainfall-free regions to rainfall regions, which supports the rainfall. Imposed forcing and sea surface temperature do not change the role of surface evaporation in rainfall processes.