Mechanism of the Centennial Subpolar North Atlantic Cooling Trend in the FGOALS‐g2 Historical Simulation

Fan, Yifei; Lü, Jianhua; Li, Laifang

doi:10.1029/2021jc017511

Cited by 11 publications

(6 citation statements)

References 42 publications

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“…4d vs a ). This is consistent with studies showing that T NA can be driven by external radiative forcing, or more general, the atmospheric forcing without an explicit role of AMOC change 21 , 22 , 48 , 49 . In contrast to T NA , the SSS indices show little response to volcanic and stratospheric ozone forcing (Fig.…”

Section: Resultssupporting

confidence: 92%

Likely accelerated weakening of Atlantic overturning circulation emerges in optimal salinity fingerprint

Zhu

Liu²,

Zhang³

et al. 2023

Nat Commun

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The long-term response of the Atlantic meridional overturning circulation (AMOC) to anthropogenic forcing has been difficult to detect from the short direct measurements available due to strong interdecadal variability. Here, we present observational and modeling evidence for a likely accelerated weakening of the AMOC since the 1980s under the combined forcing of anthropogenic greenhouse gases and aerosols. This likely accelerated AMOC weakening signal can be detected in the AMOC fingerprint of salinity pileup remotely in the South Atlantic, but not in the classic warming hole fingerprint locally in the North Atlantic, because the latter is contaminated by the “noise” of interdecadal variability. Our optimal salinity fingerprint retains much of the signal of the long-term AMOC trend response to anthropogenic forcing, while dynamically filtering out shorter climate variability. Given the ongoing anthropogenic forcing, our study indicates a potential further acceleration of AMOC weakening with associated climate impacts in the coming decades.

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Section: Resultssupporting

confidence: 92%

Likely accelerated weakening of Atlantic overturning circulation emerges in optimal salinity fingerprint

Zhu

Liu²,

Zhang³

et al. 2023

Nat Commun

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“…Although the observed North Atlantic cold blob extends further south to 40N, atmospheric forcing principally contributes to the northern portion of the cold blob, as the atmosphere-forced cooling is concentrated on the north of 50N, which is approximately the latitude of the inter-gyre boundary. SSTAs south of 50N are predominantly subject to the influence of changes in AMOCassociated ocean heat transport, as suggested by previous model studies (Keil et al 2020;Fan et al 2021). Additionally, the southward Ekman transport induced by strong surface westerlies over the inter-gyre boundary could spread the subpolar cooling anomalies further south.…”

Section: North Atlantic Ssta Trend In Response To 𝑄 Atmo Changementioning

confidence: 54%

“…The other argument is that the cold blob might not be a sole result of decreased northward ocean heat transport due to the AMOC decline. A model-based study suggests that the AMOC weakening contributes less than 30% of the cold blob in terms of its intensity and spatial extent (Fan et al 2021). In addition, the timing of the cold blob precedes the simulated AMOC decline (Drijfhout et al 2012).…”

Section: Introductionmentioning

confidence: 99%

North Atlantic Oscillation contributes to the subpolar North Atlantic cooling in the past century

et al. 2023

Self Cite

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Sea surface temperature (SST) in the subpolar North Atlantic has significantly decreased at a rate of -0.39 (±0.23) K/century during 1900-2020, which runs counter to global warming due to anthropogenic forcing. The cooling in the subpolar North Atlantic, known as the North Atlantic cold blob, could be driven by a host of mechanisms involving both the ocean and atmosphere.Here, we present evidence that changes in the atmospheric circulation over the North Atlantic, in particular a centennial trend towards a more positive phase of the North Atlantic Oscillation (NAO), could have contributed to the cold blob. The positive NAO intensifies the surface wind over the subpolar North Atlantic and induces excessive heat loss from the air-sea interface.According to an idealized mixed layer heat balance model, the NAO induced heat loss alone cools the subpolar North Atlantic by 0.26 K/century, which explains 67% of the observed cold blob SST trend. Thus, besides ocean circulation, including the slowdown of the Atlantic Meridional Overturning Circulation, the large-scale atmospheric circulation might have played an equally important role in prompting the century-long SST changes in the subpolar North Atlantic.

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“…Another recent study 8 showed that the atmosphere can contribute approximately 50% of the observed cooling trend over the NAWH due to stronger local westerlies in response to external forcing that enhance heat loss from the ocean through turbulent heat fluxes. A past study 9 also indicated that cold blobs, equivalent to the NAWH, are due to reduced heat transport by surface turbulent heat fluxes and ocean currents, and that AMOC slowdowns make only a marginal contribution to cold blobs. These suggested various theories indicate that the mechanism of the NAWH formation by the warming climate is still under discussion.…”

Section: Introductionmentioning

confidence: 99%

Formation of the North Atlantic Warming Hole by reducing anthropogenic sulphate aerosols

Kusakabe

Takemura

2023

Sci Rep

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The North Atlantic Warming Hole (NAWH) has been observed and predicted due to the increase in carbon dioxide (CO2) concentration. If sulphate aerosols, which have a cooling effect on the atmosphere, are reduced by air pollution control, the NAWH may form as it would if CO2 concentrations increased. In this study, sensitivity experiments using a coupled atmosphere–ocean-aerosol model were conducted by varying the amount of sulphur dioxide (SO2) emissions, a precursor of sulphate which is the primary anthropogenic aerosol in the atmosphere, to analyse the changes in the ocean temperature, salinity, and density. The results showed that although the spatial patterns of the NAWH due to the changes in SO2 emissions was similar to that due to the changes in the CO2 concentrations, the magnitude of the shifts in the ocean parameters due to the changes in SO2 emissions is larger even when changes in global mean temperature are comparable. This can be due to the spatial concentration of sulphate aerosols in the mid-latitudes of the Northern Hemisphere, resulting larger changes in the heat transport from the south on the Gulf Stream and the North Atlantic Current along with changes in freshwater inflow from the Arctic through the Labrador Sea.

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Mechanism of the Centennial Subpolar North Atlantic Cooling Trend in the FGOALS‐g2 Historical Simulation

Cited by 11 publications

References 42 publications

Likely accelerated weakening of Atlantic overturning circulation emerges in optimal salinity fingerprint

Likely accelerated weakening of Atlantic overturning circulation emerges in optimal salinity fingerprint

North Atlantic Oscillation contributes to the subpolar North Atlantic cooling in the past century

Formation of the North Atlantic Warming Hole by reducing anthropogenic sulphate aerosols

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