Sub-Tropical Aerosols Enhance Tropical Cloudiness—A Remote Aerosol-Cloud Lifetime Effect

Abstract

Clouds' susceptibility to aerosols is considered to be a leading source of uncertainty in climate research. An inability to account simultaneously for the large range of scales involved in cloud-aerosol-climate interactions has hindered the progress of research. In this study, using a novel system of idealized large-eddy-simulations that explicitly resolves clouds but also accounts, in an idealized manner, for large-scale changes in the thermodynamic and dynamic conditions and for inter-cloud regime coupling, it is shown that aerosol perturbation in the sub-tropics increases cloudiness in the tropics. Specifically, aerosol-driven sub-tropical rain suppression leads to increased advection of cold and moist air from the sub-tropics to the tropics, thus enhancing tropical cloudiness. The increased tropical cloudiness has a strong cooling effect by reflecting more of the incoming solar radiation. The classical “aerosol-cloud lifetime effect” is shown here to have a small local effect (in the sub-tropics) but a strong remote effect (sub-tropical aerosols increase cloudiness in the tropics), thus widening the concept of cloud adjustments to aerosol perturbation.