Here we investigate the role of the atmospheric circulation in the Atlantic Meridional Overturning Circulation (AMOC) by comparing a fully‐coupled large ensemble, a forced‐ocean simulation, and new experiments using a fully‐coupled global climate model where winds above the boundary layer are nudged toward reanalysis. When winds are nudged north of 45°N, agreement with RAPID array observations of AMOC at 26.5°N improves across several metrics. The phasing of interannual variability is well‐captured due to the response of the local Ekman component in both wind‐nudging and forced‐ocean simulations, however the variance remains underestimated. The mean AMOC strength is substantially reduced relative to the fully‐coupled model large ensemble, which is biased high, due to the impact of winds on surface buoyancy fluxes over the subpolar gyre. Nudging winds toward observations also reduces the 1979–2016 trend in AMOC, suggesting that improvement in the representation of the high‐latitude atmosphere is important for projecting long‐term AMOC changes.
The relationship between Atlantic meridional overturning circulation (AMOC) variability and high‐latitude North Atlantic buoyancy changes is complicated by the latter both driving, and responding to, AMOC changes. A maximum covariance analysis applied to a 1,201‐year preindustrial control simulation reveals two leading modes that separate these two distinct roles of North Atlantic temperature and salinity as related to AMOC variability. A linear combination of the two modes accounts for most of the variation of a widely used AMOC index. The same analysis applied to another control simulation known to possess two distinct regimes of AMOC variability—oscillatory and red‐noise—suggests that the North Atlantic buoyancy‐forced AMOC variability is present in both regimes but is weaker in the latter, and moreover there is pronounced multidecadal/centennial AMOC behavior in the latter regime that is unrelated to North Atlantic buoyancy forcing.
more » « less- NSF-PAR ID:
- 10367571
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 48
- Issue:
- 14
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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