scholarly journals Multidecadal Ocean Temperature and Salinity Variability in the Tropical North Atlantic: Linking with the AMO, AMOC, and Subtropical Cell

2013 ◽  
Vol 26 (16) ◽  
pp. 6137-6162 ◽  
Author(s):  
Chunzai Wang ◽  
Liping Zhang
Keyword(s):  
Temperature Variation ◽  
North Atlantic ◽  
Meridional Overturning Circulation ◽  
Cmip5 Models ◽  
Ocean Temperature ◽  
Surface Warming ◽  
Subsurface Ocean ◽  
Tropical North Atlantic ◽  
Current Variation ◽  
Subtropical Cell

Abstract The Atlantic multidecadal oscillation (AMO) is characterized by the sea surface warming (cooling) of the entire North Atlantic during its warm (cold) phase. Both observations and most of the phase 5 of the Coupled Model Intercomparison Project (CMIP5) models also show that the warm (cold) phase of the AMO is associated with a surface warming (cooling) and a subsurface cooling (warming) in the tropical North Atlantic (TNA). It is further shown that the warm phase of the AMO corresponds to a strengthening of the Atlantic meridional overturning circulation (AMOC) and a weakening of the Atlantic subtropical cell (STC), which both induce an anomalous northward current in the TNA subsurface ocean. Because the mean meridional temperature gradient of the subsurface ocean is positive because of the temperature dome around 9°N, the advection by the anomalous northward current cools the TNA subsurface ocean during the warm phase of the AMO. The opposite is true during the cold phase of the AMO. It is concluded that the anticorrelated ocean temperature variation in the TNA associated with the AMO is caused by the meridional current variation induced by variability of the AMOC and STC, but the AMOC plays a more important role than the STC. Observations do not seem to show an obvious anticorrelated salinity relation between the TNA surface and subsurface oceans, but most of CMIP5 models simulate an out-of-phase salinity variation. Similar to the temperature variation, the mechanism is the salinity advection by the meridional current variation induced by the AMOC and STC associated with the AMO.

scholarly journals Re-emergence of North Atlantic subsurface ocean temperature anomalies in a seasonal forecast system

2019 ◽  
Vol 53 (7-8) ◽  
pp. 4799-4820 ◽  
Author(s):  
Jeremy P. Grist ◽  
Bablu Sinha ◽  
Helene. T. Hewitt ◽  
Aurélie Duchez ◽  
Craig MacLachlan ◽  
...  
Keyword(s):  
North Atlantic ◽  
Seasonal Forecast ◽  
Ocean Temperature ◽  
Forecast System ◽  
Temperature Anomalies ◽  
Subsurface Ocean

scholarly journals Climatic impacts of fresh water hosing under Last Glacial Maximum conditions: a multi-model study

2013 ◽  
Vol 9 (2) ◽  
pp. 935-953 ◽  
Author(s):  
M. Kageyama ◽  
U. Merkel ◽  
B. Otto-Bliesner ◽  
M. Prange ◽  
A. Abe-Ouchi ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Fresh Water ◽  
North Atlantic ◽  
Greenland Ice Sheet ◽  
Meridional Overturning Circulation ◽  
Last Glacial ◽  
The North ◽  
Tropical North Atlantic ◽  
The North Atlantic ◽  
The Impact

Abstract. Fresh water hosing simulations, in which a fresh water flux is imposed in the North Atlantic to force fluctuations of the Atlantic Meridional Overturning Circulation, have been routinely performed, first to study the climatic signature of different states of this circulation, then, under present or future conditions, to investigate the potential impact of a partial melting of the Greenland ice sheet. The most compelling examples of climatic changes potentially related to AMOC abrupt variations, however, are found in high resolution palaeo-records from around the globe for the last glacial period. To study those more specifically, more and more fresh water hosing experiments have been performed under glacial conditions in the recent years. Here we compare an ensemble constituted by 11 such simulations run with 6 different climate models. All simulations follow a slightly different design, but are sufficiently close in their design to be compared. They all study the impact of a fresh water hosing imposed in the extra-tropical North Atlantic. Common features in the model responses to hosing are the cooling over the North Atlantic, extending along the sub-tropical gyre in the tropical North Atlantic, the southward shift of the Atlantic ITCZ and the weakening of the African and Indian monsoons. On the other hand, the expression of the bipolar see-saw, i.e., warming in the Southern Hemisphere, differs from model to model, with some restricting it to the South Atlantic and specific regions of the southern ocean while others simulate a widespread southern ocean warming. The relationships between the features common to most models, i.e., climate changes over the north and tropical Atlantic, African and Asian monsoon regions, are further quantified. These suggest a tight correlation between the temperature and precipitation changes over the extra-tropical North Atlantic, but different pathways for the teleconnections between the AMOC/North Atlantic region and the African and Indian monsoon regions.

The Role of Aerosols in the Evolution of Tropical North Atlantic Ocean Temperature Anomalies

Science ◽  
2009 ◽  
Vol 324 (5928) ◽  
pp. 778-781 ◽  
Author(s):  
A. T. Evan ◽  
D. J. Vimont ◽  
A. K. Heidinger ◽  
J. P. Kossin ◽  
R. Bennartz
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Ocean Temperature ◽  
Temperature Anomalies ◽  
Tropical North Atlantic

scholarly journals The role of the North Atlantic overturning and deep-ocean for multi-decadal global-mean-temperature variability

2013 ◽  
Vol 4 (2) ◽  
pp. 967-1003 ◽  
Author(s):  
C. F. Schleussner ◽  
J. Runge ◽  
J. Lehmann ◽  
A. Levermann
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
Heat Content ◽  
Deep Ocean ◽  
Meridional Overturning Circulation ◽  
Cmip5 Models ◽  
Global Mean Temperature ◽  
Mean Temperature ◽  
Global Mean

Abstract. Earth's climate exhibits internal modes of variability on various time scales. Here we investigate multi-decadal variability of the Atlantic meridional overturning circulation (AMOC) in the control runs of an ensemble of CMIP5 models. By decomposing global-mean-temperature (GMT) variance into contributions of the AMOC and Northern Hemisphere sea-ice extent using a graph-theoretical statistical approach, we find the AMOC to contribute 8% to GMT variability in the ensemble mean. Our results highlight the importance of AMOC sea-ice feedbacks that explain 5% of the GMT variance, while the contribution solely related to the AMOC is found to be about 3%. As a consequence of multi-decadal AMOC variability, we report substantial variations in North Atlantic deep-ocean heat content with trends of up to 0.7 × 1022 J decade−1 that are of the order of observed changes over the last decade and consistent with the reduced GMT warming trend over this period. Although these temperature anomalies are largely density-compensated by salinity changes, we find a robust negative correlation between the AMOC and North Atlantic deep-ocean density with density lagging the AMOC by 5 to 11 yr in most models. While this would in principle allow for a self-sustained oscillatory behavior of the coupled AMOC–deep-ocean system, our results are inconclusive about the role of this feedback in the model ensemble.

scholarly journals Mid-Pliocene Atlantic Meridional Overturning Circulation simulated in PlioMIP2

2020 ◽  
Author(s):  
Zhongshi Zhang ◽  
Xiangyu Li ◽  
Chuncheng Guo ◽  
Odd Helge Otterå ◽  
Kerim H. Nisancioglu ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Heat Transport ◽  
North Atlantic ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Ocean Heat Transport ◽  
Surface Warming ◽  
The North ◽  
Meridional Overturning ◽  
The North Atlantic

Abstract. In the Pliocene Model Intercomparison Project phase 2 (PlioMIP2), coupled climate models have been used to simulate an interglacial climate during the mid-Piacenzian warm period (mPWP, 3.264 to 3.025 Ma). Here, we compare the Atlantic Meridional Overturning Circulation (AMOC), poleward ocean heat transport and sea surface warming in the Atlantic simulated with these models. In PlioMIP2, all models simulate an intensified mid-Pliocene AMOC. However, there is no consistent response in the simulated Atlantic ocean heat transport, or the depth of the Atlantic overturning cell. The models show a large spread in the simulated AMOC maximum, the Atlantic ocean heat transport, as well as the surface warming in the North Atlantic. Although a few models simulate a surface warming of ~ 8–12 ° in the North Atlantic, similar to the reconstruction from Pliocene Research, Interpretation and Synoptic Mapping (PRISM), most models underestimate this warming. The large model-spread and model-data discrepancies in the PlioMIP2 ensemble does not support the hypothesis that an intensification of the AMOC, together with an increase in northward ocean heat transport, is the dominant forcing for the mid-Pliocene warm climate.

The Potential Mechanisms of AMOC Multidecadal Periods in CMIP6/CMIP5 Preindustrial Simulations

2021 ◽  
Author(s):  
Xiaofan Ma ◽  
Gang Huang ◽  
Xichen Li ◽  
Shouwei Li
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Climate Models ◽  
Rossby Waves ◽  
Meridional Overturning Circulation ◽  
Cmip5 Models ◽  
Mean Flow ◽  
Wave Speeds ◽  
Models Comparison ◽  
Flow Effects

Abstract Observations, theoretical analyses, and climate models show that the period of multidecadal variability of the Atlantic Meridional Overturning Circulation (AMOC) is related to westward temperature propagations in the subpolar North Atlantic, which is modulated by oceanic baroclinic Rossby waves. Here, we find major periods of AMOC variability of 12-28 years and associated westward temperature propagations in the preindustrial simulations of 9 CMIP6/CMIP5 models. Comparison with observations shows that the models reasonably simulate ocean stratifications in turn oceanic Rossby waves in the subpolar North Atlantic. The timescales of Rossby waves propagating on a static background flow across the subpolar North Atlantic basin overestimate the AMOC periods. The mean flow effects involving westward geostrophic self-advection and eastward mean advection largely shorten and greatly improve the estimate of AMOC periods through increasing Rossby wave speeds. Our results illustrate the importance of considering mean flow effects on Rossby wave propagations in the estimate of AMOC periods.

Evaluation of Subtropical North Atlantic Ocean Circulation in CMIP5 Models against the Observational Array at 26.5°N and Its Changes under Continued Warming

2018 ◽  
Vol 31 (23) ◽  
pp. 9697-9718 ◽  
Author(s):  
R. L. Beadling ◽  
J. L. Russell ◽  
R. J. Stouffer ◽  
P. J. Goodman
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Deep Ocean ◽  
Meridional Overturning Circulation ◽  
Subtropical Gyre ◽  
Ekman Transport ◽  
Cmip5 Models ◽  
Upper Ocean ◽  
Near Surface ◽  
Southward Transport

Observationally based metrics derived from the Rapid Climate Change (RAPID) array are used to assess the large-scale ocean circulation in the subtropical North Atlantic simulated in a suite of fully coupled climate models that contributed to phase 5 of the Coupled Model Intercomparison Project (CMIP5). The modeled circulation at 26.5°N is decomposed into four components similar to those RAPID observes to estimate the Atlantic meridional overturning circulation (AMOC): the northward-flowing western boundary current (WBC), the southward transport in the upper midocean, the near-surface Ekman transport, and the southward deep ocean transport. The decadal-mean AMOC and the transports associated with its flow are captured well by CMIP5 models at the start of the twenty-first century. By the end of the century, under representative concentration pathway 8.5 (RCP8.5), averaged across models, the northward transport of waters in the upper WBC is projected to weaken by 7.6 Sv (1 Sv ≡ 106 m3 s−1; −21%). This reduced northward flow is a combined result of a reduction in the subtropical gyre return flow in the upper ocean (−2.9 Sv; −12%) and a weakened net southward transport in the deep ocean (−4.4 Sv; −28%) corresponding to the weakened AMOC. No consistent long-term changes of the Ekman transport are found across models. The reduced southward transport in the upper ocean is associated with a reduction in wind stress curl (WSC) across the North Atlantic subtropical gyre, largely through Sverdrup balance. This reduced WSC and the resulting decrease in the horizontal gyre transport is a robust feature found across the CMIP5 models under increased CO2 forcing.

scholarly journals Satellite Altimetry and Tide Gauge Observed Teleconnections between Long-Term Sea Level Variability in the U.S. East Coast and the North Atlantic Ocean

2019 ◽  
Vol 11 (23) ◽  
pp. 2816
Author(s):  
Qing Xu ◽  
Kai Tu ◽  
Yongcun Cheng ◽  
Weiping Wang ◽  
Yongjun Jia ◽  
...  
Keyword(s):  
Sea Level ◽  
North Atlantic ◽  
Satellite Altimetry ◽  
North Atlantic Ocean ◽  
Tide Gauge ◽  
Atlantic Multidecadal Oscillation ◽  
Meridional Overturning Circulation ◽  
Sea Level Variability ◽  
Tropical North Atlantic ◽  
Cape Hatteras

Rising sea levels amplify the threat and magnitude of storm surges in coastal areas. The U.S. east coast region north of Cape Hatteras has shown a significant sea level rise acceleration and is believed to be a “hot-spot” for accelerating tidal flooding. To better understand the forcing mechanism of long-term regional sea level change, in order to more efficiently implement local sea level rise adaptation and mitigation measures, this work investigated the teleconnections between low-frequency sea level variability in the coastal region north of Cape Hatteras and the subpolar/tropical North Atlantic Ocean by using tide gauge measurements, satellite altimetry data and a sea level reconstruction dataset. The correlation analysis demonstrates that the tide-gauge measured sea level variability in the area north of Cape Hatteras is highly and positively correlated with that observed by satellite altimetry in the subpolar and tropical North Atlantic between 1993 and 2002. Over the following decade (2003–2012), the phase of the teleconnection in the subpolar region was reversed and the spatio-temporal correlation in the tropical North Atlantic was enhanced. Furthermore, the positive correlation in the region north of Cape Hatteras’s near shore area is strengthened, while the negative correlation in the Gulf Stream front region is weakened. The North Atlantic Oscillation and Atlantic Multidecadal Oscillation, which affect variations of the Atlantic Meridional Overturning Circulation and Gulf Stream, were shown to have significant impacts on the decadal changes of the teleconnections. Coherent with satellite altimetry data, the reconstructed sea level dataset in the 20th century exhibits similar spatial correlation patterns with the Atlantic Meridional Overturning Circulation, North Atlantic Oscillation and Atlantic Multidecadal Oscillation indices.

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