An Energetic View on the Geographical Dependence of the Fast Aerosol Radiative Effects on Precipitation

By interacting with radiation, aerosols perturb the Earth’s energy budget and thus the global precipitation amount. It was previously shown that aerosol-radiation interactions lead to a reduction in the global-mean precipitation amount. We have further demonstrated in aqua-planet simulations that the local response to absorbing aerosols differs between the tropics and the extra-tropics. In this study we incorporate an energy budget perspective to further examine the latitudinal-dependence of the effect of aerosol-radiation interaction on precipitation in idealized global simulations. We demonstrate that the transition between a positive local precipitation response in the tropics and a negative local precipitation response in the extra-tropics occurs at relatively low latitudes (∼10°), indicating a transition between the deep-tropics (in which the Coriolis force is low, hence direct thermally driven circulation, and associated divergence/convergence of energy/moisture, can form as a result of the diabatic-heating) and their surroundings. In addition, we gradually increase the level of complexity of the simulations and demonstrate that, in the case of absorbing aerosols, the effect of land is to counteract some of the response both inside and outside the deep-tropics due to the reduction in surface latent-heat flux that opposes the diabatic-heating. The effect of scattering aerosols is also examined and demonstrates a decrease in precipitation over land in both the tropics and extra-tropics and no effect over the ocean. Finally, we examine these results in a more realistic set-up and demonstrate that, although the physical mechanisms still operate, they are not significant enough to be discerned from the model’s natural-variability.