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Changes in External Forcings Drive Divergent AMOC Responses Across CESM Generations
  • Michael Robert Needham,
  • Douglas D Falter,
  • David Allan Randall
Michael Robert Needham
Colorado State University

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Douglas D Falter
Iowa State University
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David Allan Randall
Colorado State University
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The Atlantic meridional overturning circulation (AMOC) in many CMIP6 models has been shown to be overly-sensitive to anthropogenic aerosol forcing, and it has been speculated that this is due to the inclusion of aerosol indirect effects for the first time in many models of that generation. We analyze the AMOC response in a newly-released ensemble of historic simulations performed with CESM2 and forced by the older CMIP5 input datasets (CESM2-CMIP5). This AMOC response is then compared to the CESM1 large ensemble (CESM1-LE, forced by the older CMIP5 inputs) and the CESM2 large ensemble (CESM2-LE, forced by the newer CMIP6 inputs). A key conclusion, only made possible by this experimental setup, is that changes in modeled aerosol-indirect effects cannot explain the differences in turbulent fluxes between CESM1-LE and CESM2-LE. Instead, differences in surface turbulent heat fluxes from changes in model inputs likely drive the different AMOC responses.
21 Sep 2023Submitted to ESS Open Archive
30 Sep 2023Published in ESS Open Archive