The Sensitivity of the Water Vapor Budget to SSTs and Aerosols within Radiative Equilibrium Experiments

Much can be learned about cloud-radiation feedbacks and the organization and structure of convection within the tropical atmosphere from numerical simulations of radiative-convective equilibrium (RCE). Past studies have demonstrated that as RCE simulations evolve, self-sustaining moist and dry regions develop as deep convection aggregates in the moist regions. The final balanced state is characterized by the trimodal distribution of convection within the regions of high precipitable water, while populations of boundary layer clouds are evident in the low precipitable water zones. The vertical and horizontal redistribution of water between the regions is critical to the self-sustaining nature of these moist and dry regions. A number of factors can influence the redistribution of water, and hence the structure and aggregation of convection. Variations in SST influence the surface fluxes of energy and water vapor and represent proxies of different climatic states, while the presence of aerosols influences the absorption of radiation and various cloud processes. Both of these factors could therefore impact the equilibrium state and the associated water vapor budget. The goal of this research is to assess the influence of variations in SST and aerosols on the water vapor budget within the moist and dry regions. In order to achieve this goal, large-domain, high-resolution RCE simulations have been conducted in which the lower oceanic boundary, which is fixed at 300K in the control simulation, was varied from 298 to 302K. Additional tests have also been conducted in which the aerosol loading was varied from clean to polluted conditions. Analysis of the impacts of SST and aerosols on the water vapor budget within the moist and dry regions will be presented.