Influence of low-cloud radiative effects on tropical circulation and precipitation

Low-level clouds, which constitute the most prevalent cloud type over tropical oceans, exert a radiative cooling within the planetary boundary layer. By using an atmospheric general circulation model, we investigate the role that this cloud radiative cooling plays in the present-day climate. Low-cloud radiative effects are found to increase the tropics-wide precipitation, to strengthen the winds at the surface of the tropical oceans, and to amplify the atmospheric overturning circulation. An analysis of the water and energy budgets of the atmosphere reveals that most of these effects arises from the strong coupling of cloud-radiative cooling with turbulent fluxes at the ocean surface. The impact of cloud-radiative effects on atmospheric dynamics and precipitation is shown to occur on very short time scales (a few days). Therefore, short-term atmospheric forecasts constitute a valuable framework for evaluating the interactions between cloud processes and atmospheric dynamics, and for assessing their dependence on model physics.