Contrasting Response of Precipitation to Aerosol Perturbation in the Tropics and Extratropics Explained by Energy Budget Considerations

Precipitation plays a crucial role in the Earth's energy balance, the water cycle, and the global atmospheric circulation. Aerosols, by direct interaction with radiation and by serving as cloud condensation nuclei, may affect clouds and rain formation. This effect can be examined in terms of energetic constraints, that is, any aerosol-driven diabatic heating/ cooling of the atmosphere will have to be balanced by changes in precipitation, radiative fluxes, or divergence of dry static energy. Using an aqua-planet general circulation model (GCM), we show that tropical and extratropical precipitation have contrasting responses to aerosol perturbations. This behavior can be explained by contrasting ability of the atmosphere to diverge excess dry static energy in the two different regions. It is shown that atmospheric heating in the tropics leads to large-scale thermally driven circulation and a large increase in precipitation, while the excess energy from heating in the extratropics is constrained due to the effect of the Coriolis force, causing the precipitation to decrease. Plain Language Summary Precipitation, as the Earth's only natural source of fresh water, is of great importance for society. Climate change, besides changing the mean surface temperature and its distribution, is expected to change the precipitation's temporal and spatial distribution and, to a lesser extent, the global mean precipitation. One important agent in precipitation changes is anthropogenic aerosols. In this paper we study the response of precipitation to aerosol perturbations at different latitudes. Previously, it was proposed that aerosols drive a slowdown of the hydrological cycle. In addition, it was shown that, due to energy budget conservation, absorbing aerosols leads to a reduction in the global mean precipitation. Here we show that the response in the tropics is the opposite of the global mean response and of the extratropical response. Specifically, we show that the same aerosol perturbation generally increases precipitation in the tropics and decreases precipitation in the extratropics. This behavior can be explained by the contrasting ability of the atmosphere to diverge excess dry static energy in the tropics and extratropics. We also show that local aerosol perturbations could affect precipitation in remote regions due to a formation of large-scale circulation.