Anthropogenic aerosol interacts strongly with incoming solar radiation, perturbing Earth's energy budget and precipitation on both local and global scales. Understanding these changes in precipitation has proven particularly difficult for the case of absorbing aerosol, which absorbs a significant amount of incoming solar radiation and hence acts as a source of localized diabatic heating to the atmosphere. In this work, we use an ensemble of atmosphere-only climate model simulations forced by identical absorbing aerosol perturbations in different geographical locations across the globe to develop a basic physical understanding of how this localized heating impacts the atmosphere and how these changes impact on precipitation both globally and locally. In agreement with previous studies we find that absorbing aerosol causes a decrease in global-mean precipitation, but we also show that even for identical aerosol optical depth perturbations, the global-mean precipitation change varies by over an order of magnitude depending on the location of the aerosol burden. Our experiments also demonstrate that the local precipitation response to absorbing aerosol is opposite in sign between the tropics and the extratropics, as found by previous work. We then show that this contrasting response can be understood in terms of different mechanisms by which the large-scale circulation responds to heating in the extratropics and in the tropics. We provide a simple theory to explain variations in the local precipitation response to absorbing aerosol in the tropics. Our work highlights that the spatial pattern of absorbing aerosol and its interactions with circulation are a key determinant of its overall climate impact and must be taken into account when developing our understanding of aerosol-climate interactions.
Bibliographical noteFunding Information:
Acknowledgments. A.I.L. Williams acknowledges funding from the Natural Environment Research Council, Oxford DTP, Award NE/S007474/1. D.W.P. acknowledges funding from NERC Project NE/S005390/1 (ACRUISE) as well as from the European Union’s Horizon 2020 research and innovation programme iMIRACLI under Marie Skłodowska-Curie Grant Agreement 860100. P.S. and G.D. were supported by the European Research Council (ERC) project Constraining the Effects of Aerosols on Precipitation (RECAP) under the European Union’s Horizon 2020 research and innovation programme with Grant Agreement 724602. P.S. additionally acknowledges funding from the FORCeS and NextGEMs project under the European Union’s Horizon 2020 research programme with Grant Agreements 821205 and 101003470, respectively. G.D. also acknowledges funding from the Israeli Science Foundation Grant 1419/21. The simulations were performed using the ARCHER2 U.K. National Supercomputing Service. Data analysis was performed on JASMIN, the U.K. collaborative data analysis facility, and LOTUS, the associated high performance batch compute cluster.
© 2023 American Meteorological Society.
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