Will Global Warming Suppress North Atlantic Tripole Decadal Variability?

Abstract In this paper, the modulations of the North Atlantic tripole (NAT) decadal variability from global warming are studied by conducting a series of coupled ocean–atmosphere experiments using the Fast Ocean Atmosphere Model (FOAM). The model reasonably captures the observed NAT decadal variability with a preferred time scale of about 11 years. With the aid of partial-blocking and partial-coupling experiments, it is found that the NAT decadal cycle can be attributed to oceanic planetary wave adjustment in the subtropical basin and ocean–atmosphere coupling over the North Atlantic. In a doubled CO2 experiment, the spatial pattern of the NAT is preserved; however, the decadal cycle is significantly suppressed. This suppression appears to be associated with the acceleration of oceanic planetary waves due to an increase of buoyancy frequency in global warming. This shortens the time from a decadal to an interannual time scale for the first-mode baroclinic Rossby waves to cross the subtropical North Atlantic basin, the primary memory for the NAT decadal variability in the model. The modeling study also found that the global warming does not modulate the North Atlantic air–sea coupling significantly, but it may be model dependent.

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On the Structure and Teleconnections of North Atlantic Decadal Variability

Journal of Climate ◽

10.1175/2011jcli3478.1 ◽

2011 ◽

Vol 24 (9) ◽

pp. 2209-2223 ◽

Cited By ~ 12

Author(s):

Francisco J. Álvarez-García ◽

María J. OrtizBevia ◽

William D. CabosNarvaez

Keyword(s):

North Atlantic ◽

Time Scale ◽

Decadal Variability ◽

The North ◽

The Pacific ◽

Tropical North Atlantic ◽

Decadal Variations ◽

The Pacific Ocean ◽

The North Atlantic ◽

The North Atlantic Oscillation

Abstract Decadal variability in the North Atlantic has been associated in the literature with a tripolar pattern of sea surface temperature (SST) anomalies that show one sign in the western midlatitudinal North Atlantic and the opposite in the subpolar and tropical North Atlantic. The present analysis of observed SST from 1870 to 2009 leads to the dissection of the SST tripole into two components, each with a different time scale in the decadal band and different teleconnections in the Atlantic basin; while the subpolar and tropical poles present quasi-decadal variations with a period of about 9 years, essentially uncorrelated with other parts of the basin, the center of action in the western midlatitudes is characterized by a longer time scale of about 14 years and significant correlations with the tropical South Atlantic and the Norwegian and North Sea(s). The 9-yr period variations are associated with an atmospheric configuration resembling the east Atlantic pattern, whereas the 14-yr period fluctuations seem to be related to the North Atlantic Oscillation pattern. Each component also bears a different relationship with the decadal variability in the Pacific Ocean.

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North Atlantic Decadal Variability: Air–Sea Coupling, Oceanic Memory, and Potential Northern Hemisphere Resonance*

Journal of Climate ◽

10.1175/jcli-3264.1 ◽

2005 ◽

Vol 18 (2) ◽

pp. 331-349 ◽

Cited By ~ 61

Author(s):

Lixin Wu ◽

Zhengyu Liu

Keyword(s):

Time Scales ◽

Negative Feedback ◽

North Atlantic ◽

Decadal Variability ◽

Stochastic Forcing ◽

The North ◽

The Pacific ◽

Model Control ◽

Ocean Atmosphere ◽

The North Atlantic

Abstract In this paper, the causes and mechanisms of North Atlantic decadal variability are explored in a series of coupled ocean–atmosphere simulations. The model captures the major features of the observed North Atlantic decadal variability. The North Atlantic SST anomalies in the model control simulation exhibit a prominent decadal cycle of 12–16 yr, and a coherent propagation from the western subtropical Atlantic to the subpolar region. A series of additional modeling experiments are conducted in which the air–sea coupling is systematically modified in order to evaluate the importance of air–sea coupling for the North Atlantic decadal variability being studied. This shall be referred to as “modeling surgery.” The results suggest the critical role of ocean–atmosphere coupling in sustaining the North Atlantic decadal oscillation at selected time scales. The coupling in the North Atlantic is characterized by a robust North Atlantic Oscillation (NAO)-like atmospheric response to the SST tripole anomaly, which tends to intensify the SST anomaly and, meanwhile, also provide a delayed negative feedback. This delayed negative feedback is predominantly associated with the adjustment of the subtropical gyre in response to the anomalous wind stress curl in the subtropical Atlantic. Atmospheric stochastic forcing can drive SST patterns similar to those in the fully coupled ocean–atmosphere system, but fails to generate any preferred decadal time scales. The simulated North Atlantic decadal variability, therefore, can be viewed as a coupled ocean–atmosphere mode under the influence of stochastic forcing. This modeling study also suggests some potential resonance between the Pacific and the North Atlantic decadal fluctuations mediated by the atmosphere. The modeling surgery indicates that the Pacific climate, although not a necessary precondition, can impact the North Atlantic climate variability substantially.

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The stability of the North Atlantic thermohaline circulation in a coupled ocean-atmosphere general circulation model

Climate Dynamics ◽

10.1007/s003820050169 ◽

1997 ◽

Vol 13 (5) ◽

pp. 325-347 ◽

Cited By ~ 199

Author(s):

A. Schiller ◽

U. Mikolajewicz ◽

R. Voss

Keyword(s):

North Atlantic ◽

General Circulation ◽

Thermohaline Circulation ◽

Circulation Model ◽

The North ◽

Ocean Atmosphere ◽

Atmosphere General Circulation Model ◽

The North Atlantic ◽

Atlantic Thermohaline Circulation ◽

The Stability

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Interannual-to-decadal variability of the North Atlantic from an ocean data assimilation system

Climate Dynamics ◽

10.1007/s00382-004-0453-6 ◽

2004 ◽

Vol 23 (5) ◽

pp. 531-546 ◽

Cited By ~ 21

Author(s):

S. Masina ◽

P. Di Pietro ◽

A. Navarra

Keyword(s):

Data Assimilation ◽

North Atlantic ◽

Decadal Variability ◽

The North ◽

Ocean Data Assimilation ◽

The North Atlantic ◽

Data Assimilation System ◽

Assimilation System

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Understanding Bjerknes Compensation in Meridional Heat Transports and the Role of Freshwater in a Warming Climate

Journal of Climate ◽

10.1175/jcli-d-17-0587.1 ◽

2018 ◽

Vol 31 (12) ◽

pp. 4791-4806 ◽

Cited By ~ 4

Author(s):

Qianzi Yang ◽

Yingying Zhao ◽

Qin Wen ◽

Jie Yao ◽

Haijun Yang

Keyword(s):

Global Warming ◽

North Atlantic ◽

Coupled Model ◽

Phase Changes ◽

Box Model ◽

Freshwater Flux ◽

The North ◽

Warming Climate ◽

Transient Period ◽

The North Atlantic

The Bjerknes compensation (BJC) under global warming is studied using a simple box model and a coupled Earth system model. The BJC states the out-of-phase changes in the meridional atmosphere and ocean heat transports. Results suggest that the BJC can occur during the transient period of global warming. During the transient period, the sea ice melting in the high latitudes can cause a significant weakening of the Atlantic meridional overturning circulation (AMOC), resulting in a cooling in the North Atlantic. The meridional contrast of sea surface temperature would be enhanced, and this can eventually enhance the Hadley cell and storm-track activities in the Northern Hemisphere. Accompanied by changes in both ocean and atmosphere circulations, the northward ocean heat transport in the Atlantic is decreased while the northward atmosphere heat transport is increased, and the BJC occurs in the Northern Hemisphere. Once the freshwater influx into the North Atlantic Ocean stops, or the ocean even loses freshwater because of strong heating in the high latitudes, the AMOC would recover. Both the atmosphere and ocean heat transports would be enhanced, and they can eventually recover to the state of the control run, leading to the BJC to become invalid. The above processes are clearly demonstrated in the coupled model CO2 experiment. Since it is difficult to separate the freshwater effect from the heating effect in the coupled model, a simple box model is used to understand the BJC mechanism and freshwater’s role under global warming. In a warming climate, the freshwater flux into the ocean can cool the global surface temperature, mitigating the temperature rise. Box model experiments indicate clearly that it is the freshwater flux into the North Atlantic that causes out-of-phase changes in the atmosphere and ocean heat transports, which eventually plays a stabilizing role in global climate change.

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Near-surface wind speeds in ERA5: Climatology, decadal variability and long-term trends

10.5194/egusphere-egu21-4472 ◽

2021 ◽

Author(s):

Terhi K. Laurila ◽

Victoria A. Sinclair ◽

Hilppa Gregow

Keyword(s):

Iberian Peninsula ◽

North Atlantic ◽

Decadal Variability ◽

Surface Wind ◽

Northern Europe ◽

Near Surface ◽

Wind Speeds ◽

The North ◽

The North Atlantic

The knowledge of long-term climate and variability of near-surface wind speeds is essential and widely used among meteorologists, climate scientists and in industries such as wind energy and forestry. The new high-resolution ERA5 reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF) will likely be used as a reference in future climate projections and in many wind-related applications. Hence, it is important to know what is the mean climate and variability of wind speeds in ERA5.We present the monthly 10-m wind speed climate and decadal variability in the North Atlantic and Europe during the 40-year period (1979-2018) based on ERA5. In addition, we examine temporal time series and possible trends in three locations: the central North Atlantic, Finland and Iberian Peninsula. Moreover, we investigate what are the physical reasons for the decadal changes in 10-m wind speeds.The 40-year mean and the 98th percentile wind speeds show a distinct contrast between land and sea with the strongest winds over the ocean and a seasonal variation with the strongest winds during winter time. The winds have the highest values and variabilities associated with storm tracks and local wind phenomena such as the mistral. To investigate the extremeness of the winds, we defined an extreme find factor (EWF) which is the ratio between the 98th percentile and mean wind speeds. The EWF is higher in southern Europe than in northern Europe during all months. Mostly no statistically significant linear trends of 10-m wind speeds were found in the 40-year period in the three locations and the annual and decadal variability was large.The windiest decade in northern Europe was the 1990s and in southern Europe the 1980s and 2010s. The decadal changes in 10-m wind speeds were largely explained by the position of the jet stream and storm tracks and the strength of the north-south pressure gradient over the North Atlantic. In addition, we investigated the correlation between the North Atlantic Oscillation (NAO) and the Atlantic Multi-decadal Oscillation (AMO) in the three locations. The NAO has a positive correlation in the central North Atlantic and Finland and a negative correlation in Iberian Peninsula. The AMO correlates moderately with the winds in the central North Atlantic but no correlation was found in Finland or the Iberian Peninsula. Overall, our study highlights that rather than just using long-term linear trends in wind speeds it is more informative to consider inter-annual or decadal variability.

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Timing and structure of the Younger Dryas event and its underlying climate dynamics

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2007869117 ◽

2020 ◽

Vol 117 (38) ◽

pp. 23408-23417

Author(s):

Hai Cheng ◽

Haiwei Zhang ◽

Christoph Spötl ◽

Jonathan Baker ◽

Ashish Sinha ◽

...

Keyword(s):

Southern Hemisphere ◽

North Atlantic ◽

Time Scale ◽

Asian Monsoon ◽

Younger Dryas ◽

Tropical Pacific ◽

Last Glacial ◽

The North ◽

The North Atlantic ◽

The Last Glacial

The Younger Dryas (YD), arguably the most widely studied millennial-scale extreme climate event, was characterized by diverse hydroclimate shifts globally and severe cooling at high northern latitudes that abruptly punctuated the warming trend from the last glacial to the present interglacial. To date, a precise understanding of its trigger, propagation, and termination remains elusive. Here, we present speleothem oxygen-isotope data that, in concert with other proxy records, allow us to quantify the timing of the YD onset and termination at an unprecedented subcentennial temporal precision across the North Atlantic, Asian Monsoon-Westerlies, and South American Monsoon regions. Our analysis suggests that the onsets of YD in the North Atlantic (12,870 ± 30 B.P.) and the Asian Monsoon-Westerlies region are essentially synchronous within a few decades and lead the onset in Antarctica, implying a north-to-south climate signal propagation via both atmospheric (decadal-time scale) and oceanic (centennial-time scale) processes, similar to the Dansgaard–Oeschger events during the last glacial period. In contrast, the YD termination may have started first in Antarctica at ∼11,900 B.P., or perhaps even earlier in the western tropical Pacific, followed by the North Atlantic between ∼11,700 ± 40 and 11,610 ± 40 B.P. These observations suggest that the initial YD termination might have originated in the Southern Hemisphere and/or the tropical Pacific, indicating a Southern Hemisphere/tropics to North Atlantic–Asian Monsoon-Westerlies directionality of climatic recovery.

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