Cloud microphysical and rainfall responses to zonal perturbations of sea surface temperature: A cloud-resolving modeling study

The cloud microphysical and rainfall responses to zonal perturbations of sea surface temperature (SST) are investigated by analyzing the equilibrium simulation data (from day 31 40) obtained from a series of two-dimensional cloud-resolving simulations with a zonal model domain of 768 km. Four experiments imposed by zonal SST perturbations of wavenumbers 1 (SST29Z1), 2 (SST29Z2), 4 (SST29Z4), and 8 (SST29Z8) are compared to the control experiment imposed by zonally uniform SST (SST29). The model domain mean SST is 29 degrees C, and the two-dimensional cloud-resolving model with a cyclic lateral boundary is also imposed by zero vertical velocity and constant zonal wind. The time and model domain mean surface rain rates in SST29Z1, SST29Z2, and SST29Z8 are about 10% larger than those in SST29, whereas the mean surface rain rates in SST29Z4 and SST29 are similar. The analysis of mean surface rainfall budgets shows that local water vapor and hydrometeor changes play important roles in determining the differences and similarities in mean surface rain rate between the perturbation experiments and the control experiment. Both convective and stratiform rain rates are larger in SST29Z1 and SST29Z2 than in SST29 due to the smaller advection of rain from convective regions into raining stratiform regions and the larger vapor condensation rates associated with the larger water vapor convergence over raining stratiform regions in SST29Z1 and SST29Z2. The convective rain rates are larger in SST29Z4 and SST29Z8 than in SST29 because of the larger condensation rates associated with the larger water vapor convergence over convective regions in SST29Z4 and SST29Z8. The stratiform rain rates in SST29Z4 and SST29Z8 are smaller than in SST29 due to the smaller vapor condensation rates and smaller collection rates of cloud water by rain over raining stratiform regions in SST29Z4 and SST29Z8. (C) 2008 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in China Press. All rights reserved.