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Abstract The ocean’s role in Atlantic Multidecadal Variability (AMV) remains intensely debated. The core issue is whether AMV, as an internal climate mode, is driven by variations in Atlantic Meridional Overturning Circulation (AMOC) or by atmospheric processes. Climate models exhibit wide diversity in AMOC-AMV linkages, producing temporal correlations between 0.3-0.8, but no robust explanation for these differences exists. Here, using multi-model intercomparison and perturbation experiments, we propose a dynamical mechanism relating the strength of AMOC-AMV linkage in climate models to stratospheric temperature. This mechanism includes (1) tropospheric midlatitude jet response to stratospheric mean-state temperature anomalies in mid-latitudes and (2) resulting ocean surface density changes that alter the spatial structure of deep-water formation in the subpolar North Atlantic and hence AMOC-AMV connection. Specifically, colder stratospheric temperatures produce tighter linkage through the northward jet shifts and a stronger AMOC, with enhanced deep-water formation in the Labrador and Irminger Seas relative to the Nordic Seas. Models with a warm stratospheric bias tend to produce weaker linkage. Perturbation experiments imposing stratospheric cooling at mid to high latitudes within two independent climate models support these conclusions. Furthermore, we find that models with stronger AMOC-AMV linkage predict a stronger North Atlantic “warming hole” and weaker 21st-century Arctic amplification. We conclude that these results have significant implications for climate prediction and projections.
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Coupled Stratospheric Ozone and Atlantic Meridional Overturning Circulation Feedbacks on the Northern Hemisphere Midlatitude Jet Response to 4xCO2
Abstract Stratospheric ozone, and its response to anthropogenic forcings, provides an important pathway for the coupling between atmospheric composition and climate. In addition to stratospheric ozone’s radiative impacts, recent studies have shown that changes in the ozone layer due to 4xCO2have a considerable impact on the Northern Hemisphere (NH) tropospheric circulation, inducing an equatorward shift of the North Atlantic jet during boreal winter. Using simulations produced with the NASA Goddard Institute for Space Studies (GISS) high-top climate model (E2.2), we show that this equatorward shift of the Atlantic jet can induce a more rapid weakening of the Atlantic meridional overturning circulation (AMOC). The weaker AMOC, in turn, results in an eastward acceleration and poleward shift of the Atlantic and Pacific jets, respectively, on longer time scales. As such, coupled feedbacks from both stratospheric ozone and the AMOC result in a two-time-scale response of the NH midlatitude jet to abrupt 4xCO2forcing: a “fast” response (5–20 years) during which it shifts equatorward and a “total” response (∼100–150 years) during which the jet accelerates and shifts poleward. The latter is driven by a weakening of the AMOC that develops in response to weaker surface zonal winds that result in reduced heat fluxes out of the subpolar gyre and reduced North Atlantic Deep Water formation. Our results suggest that stratospheric ozone changes in the lower stratosphere can have a surprisingly powerful effect on the AMOC, independent of other aspects of climate change.
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- Award ID(s):
- 1902409
- PAR ID:
- 10521248
- Publisher / Repository:
- AMS
- Date Published:
- Journal Name:
- Journal of Climate
- Volume:
- 37
- Issue:
- 10
- ISSN:
- 0894-8755
- Page Range / eLocation ID:
- 2897 to 2917
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1175/JCLI-D-23-0119.1
