The role of anthropogenic aerosol forcing in the 1850–1985 strengthening of the AMOC in CMIP6 historical simulations

Robson, Jon, Menary, Matthew B., Sutton, Rowan T., Mecking, Jenny, Gregory, Jonathan M., Jones, Colin, Sinha, Bablu, Stevens, David P. ORCID: https://orcid.org/0000-0002-7283-4405 and Wilcox, Laura J. (2022) The role of anthropogenic aerosol forcing in the 1850–1985 strengthening of the AMOC in CMIP6 historical simulations. Journal of Climate, 35 (20). 3243–3263. ISSN 0894-8755

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Abstract

Previous work has shown that anthropogenic aerosol (AA) forcing drives a strengthening in the Atlantic Meridional Overturning Circulation (AMOC) in CMIP6 historical simulations over 1850–1985, but the mechanisms have not been fully understood. Across CMIP6 models, it is shown that there is a strong correlation between surface heat loss over the subpolar North Atlantic (SPNA) and the forced strengthening of the AMOC. Despite the link to AA forcing, the AMOC response is not strongly related to the contribution of anomalous downwelling surface shortwave radiation to SPNA heat loss. Rather, the spread in AMOC response is primarily due to the spread in turbulent heat loss. We hypothesize that turbulent heat loss is larger in models with strong AA forcing because the air advected over the ocean is colder and drier, in turn because of greater AA forced cooling over the continents upwind, especially North America. The strengthening of the AMOC also feeds back on itself positively in two distinct ways: by raising the sea surface temperature and hence further increasing turbulent heat loss in the SPNA, and by increasing the sea surface density across the SPNA due to increased northward transport of saline water. A comparison of key indices suggests that the AMOC response in models with strong AA forcing is not likely to be consistent with observations.

Item Type: Article
Additional Information: Funding information: This study was funded by the NERC ACSIS program (NE/N018001/1 and NE/N018044/1). JR was additionally funded by NERC via NCAS, as well as the WISHBONE (NE/T013516/1) and SNAP-DRAGON (NE/T013494/1) projects. CJ was funded by the NERC UKESM program (NE/N017978/1). Data availability statement: The CMIP6 model data used in this study were downloaded from the ESGF (e.g., https://esgf-index1.ceda.ac.uk/) and are freely available. References for the simulations used are in the online supplemental material. The binned North Atlantic subpolar surface salinity data were made freely available by the French Sea Surface Salinity Observation Service (http://www.legos.obs-mip.fr/observations/sss/). ERSST was freely available from the National Centers for Environmental Information (https://www.ncei.noaa.gov/). The Berkeley Earth Surface Temperature dataset was downloaded from https://berkeleyearth.org/data/.
Uncontrolled Keywords: aerosols,coupled models,meridional overturning circulation,north atlantic ocean,thermocline circulation,atmospheric science ,/dk/atira/pure/subjectarea/asjc/1900/1902
Faculty \ School: Faculty of Science > School of Mathematics
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Depositing User: LivePure Connector
Date Deposited: 20 Jul 2022 14:30
Last Modified: 19 Jan 2023 12:33
URI: https://ueaeprints.uea.ac.uk/id/eprint/86736
DOI: 10.1175/JCLI-D-22-0124.1

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