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

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.