An energetic view on the geographical dependence of the fast aerosol
radiative effects on precipitation
Abstract
By interacting with radiation, aerosols perturb the Earth’s energy
budget and thus the global precipitation amount. It was previously shown
that aerosols 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 demonstrate 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 unlikely to be significant enough to be discerned from
natural-variability.