Plausible Effect of Weather on Atlantic Meridional Overturning Circulation with a Coupled General Circulation Model

2018 ◽  
Vol 17 (2) ◽  
pp. 219-226
Author(s):  
Zedong Liu ◽  
Xiuquan Wan
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Circulation Model ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Coupled General Circulation Model ◽  
Overturning Circulation ◽  
Meridional Overturning

scholarly journals On the Near-Inertial Resonance of the Atlantic Meridional Overturning Circulation

2013 ◽  
Vol 43 (12) ◽  
pp. 2661-2672 ◽  
Author(s):  
Florian Sévellec ◽  
Joël J.-M. Hirschi ◽  
Adam T. Blaker
Keyword(s):  
General Circulation ◽  
Numerical Models ◽  
Circulation Model ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Resonance Phenomenon ◽  
Dimensionless Number ◽  
Overturning Circulation ◽  
Wide Range ◽  
Meridional Overturning

Abstract The Atlantic meridional overturning circulation (AMOC) is a crucial component of the global climate system. It is responsible for around a quarter of the global northward heat transport and contributes to the mild European climate. Observations and numerical models suggest a wide range of AMOC variability. Recent results from an ocean general circulation model (OGCM) in a high-resolution configuration (¼°) suggest the existence of superinertial variability of the AMOC. In this study, the validity of this result in a theoretical framework is tested. At a low Rossby number and in the presence of Rayleigh friction, it is demonstrated that, unlike a typical forced damped oscillator (which shows subinertial resonance), the AMOC undergoes both super- and subinertial resonances (except at low latitudes and for high friction). A dimensionless number Sr, measuring the ratio of ageo- to geostrophic forcing (i.e., the zonal versus meridional pressure gradients), indicates which of these resonances dominates. If Sr ≪ 1, the AMOC variability is mainly driven by geostrophic forcing and shows subinertial resonance. Alternatively and consistent with the recently published ¼° OGCM experiments, if Sr ≫ 1, the AMOC variability is mainly driven by the ageostrophic forcing and shows superinertial resonance. In both regimes, a forcing of ±1 K induces an AMOC variability of ±10 Sv (1 Sv ≡ 106 m3 s−1) through these near-inertial resonance phenomena. It is also shown that, as expected from numerical simulations, the spatial structure of the near-inertial AMOC variability corresponds to equatorward-propagating waves equivalent to baroclinic Poincaré waves. The long-time average of this resonance phenomenon, raising and depressing the pycnocline, could contribute to the mixing of the ocean stratification.

Wind-Driven Seasonal Cycle of the Atlantic Meridional Overturning Circulation

2014 ◽  
Vol 44 (6) ◽  
pp. 1541-1562 ◽  
Author(s):  
Jian Zhao ◽  
William Johns
Keyword(s):  
Seasonal Cycle ◽  
General Circulation ◽  
Numerical Models ◽  
Circulation Model ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Ekman Transport ◽  
Western Boundary ◽  
Overturning Circulation ◽  
Meridional Overturning

Abstract The dynamical processes governing the seasonal cycle of the Atlantic meridional overturning circulation (AMOC) are studied using a variety of models, ranging from a simple forced Rossby wave model to an eddy-resolving ocean general circulation model. The AMOC variability is decomposed into Ekman and geostrophic transport components, which reveal that the seasonality of the AMOC is determined by both components in the extratropics and dominated by the Ekman transport in the tropics. The physics governing the seasonal fluctuations of the AMOC are explored in detail at three latitudes (26.5°N, 6°N, and 34.5°S). While the Ekman transport is directly related to zonal wind stress seasonality, the comparison between different numerical models shows that the geostrophic transport involves a complex oceanic adjustment to the wind forcing. The oceanic adjustment is further evaluated by separating the zonally integrated geostrophic transport into eastern and western boundary currents and interior flows. The results indicate that the seasonal AMOC cycle in the extratropics is controlled mainly by local boundary effects, where either the western or eastern boundary can be dominant at different latitudes, while in the northern tropics it is the interior flow and its lagged compensation by the western boundary current that determine the seasonal AMOC variability.

scholarly journals The Onset of the Last Interglacial and Fingerprints of Transient Atlantic Meridional Overturning Circulation

2021 ◽  
Author(s):  
Paul Gierz ◽  
Gregor Knorr ◽  
Aline Govin ◽  
Emilie Capron ◽  
Nadezhda Sokolova ◽  
...  
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Circulation Model ◽  
Atlantic Meridional Overturning Circulation ◽  
Ocean General Circulation Model ◽  
Meridional Overturning Circulation ◽  
Last Interglacial ◽  
Overturning Circulation ◽  
Climate Conditions ◽  
Meridional Overturning

Abstract Transitions from glacials to interglacials are the largest climate shifts that occurred during the Quaternary. These glacial terminations are characterized by transient changes in the Atlantic Meridional Overturning Circulation (AMOC) and associated alterations in the northward heat transport. It has been a challenge to differentiate between early last interglacial or late penultimate glacial climate conditions at 129-131 ka (thousands of years before present). Neither simulations with a stable interglacial-type nor with a freshwater perturbed AMOC state have reproduced the reconstructed sea surface temperature (SST) fingerprint in the North Atlantic. As previous approaches failed to consider the highly transient nature of the climate system at ~130 ka, the potential of transient, deglaciating AMOC responses and the corresponding impact on North Atlantic SST has yet to be examined. In this study, we employ a fully coupled Atmosphere-Ocean General Circulation Model (AOGCM) equipped with a stable-oxygen isotope module to investigate the underlying AMOC dynamics at the onset of the Last Interglacial (LIG). We demonstrate that successfully capturing both the SST patterns and the calcite δ18O signature in planktonic foraminifera from North Atlantic marine sediment cores necessitates a transiently recovering AMOC. Furthermore, this critically depends on capturing the cold, glacial ocean state prior to the onset of the interglacial.

scholarly journals A coupled model study on the Atlantic Meridional Overturning Circulation under extreme atmospheric CO2 conditions

2016 ◽  
Vol 59 (2) ◽  
Author(s):  
Rita Lecci ◽  
Simona Masina ◽  
Annalisa Cherchi ◽  
Marcelo Barreiro
Keyword(s):  
Water Column ◽  
General Circulation ◽  
Circulation Model ◽  
Extreme Case ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
High Latitudes ◽  
Stable States ◽  
Overturning Circulation ◽  
Meridional Overturning

<p>This study investigates the climate sensitivity to a strong CO<span><sub>2</sub></span> atmospheric forcing focusing on the North Atlantic Ocean (NA). The analysis is based on a set of 600 years long experiments performed with a state-of-the-art coupled general circulation model (CGCM) with the 1990 reference value of atmospheric CO<span><sub>2</sub></span> multiplied by 4, 8 and 16. Extreme increases in atmospheric CO<span><sub>2</sub></span> concentration have been applied to force the climate system towards stable states with different thermo-dynamical properties and analyze how the different resulting oceanic stratification and diffusion affect the Atlantic Meridional Overturning Circulation (AMOC). The AMOC weakens in response to the induced warming with distinctive features in the extreme case: a southward shift of convective sites and the formation of a density front at mid-latitudes. The analysis of the density fluxes reveals that NA loses density at high latitudes and gains it southward of 40°N mainly due to the haline contribution. Our results indicate that the most important processes that control the AMOC are active in the high latitudes and are related to the stability of the water column. The increased ocean stratification stabilizes the ocean interior leading to a decreased vertical diffusivity, a reduction in the formation of deep water and a weaker circulation. In particular, the deep convection collapses mainly in the Labrador Sea as a consequence of the water column stratification under high latitudes freshening.</p>

scholarly journals Influence of the Multidecadal Atlantic Meridional Overturning Circulation Variability on European Climate

2006 ◽  
Vol 19 (23) ◽  
pp. 6062-6067 ◽  
Author(s):  
Holger Pohlmann ◽  
Frank Sienz ◽  
Mojib Latif
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Max Planck ◽  
Overturning Circulation ◽  
Multidecadal Variability ◽  
European Climate ◽  
Meridional Overturning

Abstract The influence of the natural multidecadal variability of the Atlantic meridional overturning circulation (MOC) on European climate is investigated using a simulation with the coupled atmosphere–ocean general circulation model ECHAM5/Max Planck Institute Ocean Model (MPI-OM). The results show that Atlantic MOC fluctuations, which go along with changes in the northward heat transport, in turn affect European climate. Additionally, ensemble predictability experiments with ECHAM5/MPI-OM show that the probability density functions of surface air temperatures in the North Atlantic/European region are affected by the multidecadal variability of the large-scale oceanic circulation. Thus, some useful decadal predictability may exist in the Atlantic/European sector.

scholarly journals Can the boundary profiles at 26° N be used to extract buoyancy-forced Atlantic Meridional Overturning Circulation signals?

Ocean Science ◽  
2020 ◽  
Vol 16 (5) ◽  
pp. 1067-1088
Author(s):  
Irene Polo ◽  
Keith Haines ◽  
Jon Robson ◽  
Christopher Thomas
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
Atlantic Meridional Overturning Circulation ◽  
Ocean General Circulation Model ◽  
Meridional Overturning Circulation ◽  
Western Boundary ◽  
Overturning Circulation ◽  
Western Atlantic ◽  
Buoyancy Forcing ◽  
Meridional Overturning

Abstract. The temporal variability of the Atlantic Meridional Overturning Circulation (AMOC) is driven both by direct wind stresses and by the buoyancy-driven formation of North Atlantic Deep Water over the Labrador Sea and Nordic Seas. In many models, low-frequency density variability down the western boundary of the Atlantic basin is linked to changes in the buoyancy forcing over the Atlantic subpolar gyre (SPG) region, and this is found to explain part of the geostrophic AMOC variability at 26∘ N. In this study, using different experiments with an ocean general circulation model (OGCM), we develop statistical methods to identify characteristic vertical density profiles at 26∘ N at the western and eastern boundaries, which relate to the buoyancy-forced AMOC. We show that density anomalies due to anomalous buoyancy forcing over the SPG propagate equatorward along the western Atlantic boundary (through 26∘ N), eastward along the Equator, and then poleward up the eastern Atlantic boundary. The timing of the density anomalies appearing at the western and eastern boundaries at 26∘ N reveals ∼ 2–3-year lags between boundaries along deeper levels (2600–3000 m). Record lengths of more than 26 years are required at the western boundary (WB) to allow the buoyancy-forced signals to appear as the dominant empirical orthogonal function (EOF) mode. Results suggest that the depth structure of the signals and the lagged covariances between the boundaries at 26∘ N may both provide useful information for detecting propagating signals of high-latitude origin in more complex models and potentially in the observational RAPID (Rapid Climate Change programme) array. However, time filtering may be needed, together with the continuation of the RAPID programme, in order to extend the time period.

A Theory of the Interhemispheric Meridional Overturning Circulation and Associated Stratification

2012 ◽  
Vol 42 (10) ◽  
pp. 1652-1667 ◽  
Author(s):  
Maxim Nikurashin ◽  
Geoffrey Vallis
Keyword(s):  
Deep Water ◽  
General Circulation ◽  
Mesoscale Eddy ◽  
Circulation Model ◽  
Meridional Overturning Circulation ◽  
Minor Role ◽  
Diapycnal Mixing ◽  
Overturning Circulation ◽  
Northern Latitudes ◽  
Meridional Overturning

Abstract A quantitative theoretical model of the meridional overturning circulation and associated deep stratification in an interhemispheric, single-basin ocean with a circumpolar channel is presented. The theory includes the effects of wind, eddies, and diapycnal mixing and predicts the deep stratification and overturning streamfunction in terms of the surface forcing and other parameters of the problem. It relies on a matching among three regions: the circumpolar channel at high southern latitudes, a region of isopycnal outcrop at high northern latitudes, and the ocean basin between. The theory describes both the middepth and abyssal cells of a circulation representing North Atlantic Deep Water and Antarctic Bottom Water. It suggests that, although the strength of the middepth overturning cell is primarily set by the wind stress in the circumpolar channel, middepth stratification results from a balance between the wind-driven upwelling in the channel and deep-water formation at high northern latitudes. Diapycnal mixing in the ocean interior can lead to warming and upwelling of deep waters. However, for parameters most representative of the present ocean mixing seems to play a minor role for the middepth cell. In contrast, the abyssal cell is intrinsically diabatic and controlled by a balance between the deep mixing-driven upwelling and the residual of the wind-driven and eddy-induced circulations in the Southern Ocean. The theory makes explicit predictions about how the stratification and overturning circulation vary with the wind strength, diapycnal diffusivity, and mesoscale eddy effects. The predictions compare well with numerical results from a coarse-resolution general circulation model.

scholarly journals Sediment <sup>231</sup>Pa/<sup>230</sup>Th as a recorder of the rate of the Atlantic meridional overturning circulation: insights from a 2-D model

2009 ◽  
Vol 6 (3) ◽  
pp. 2755-2829 ◽  
Author(s):  
Y. Luo ◽  
R. Francois ◽  
S. E. Allen
Keyword(s):  
Circulation Model ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Equatorial Atlantic ◽  
Overturning Circulation ◽  
Data Set ◽  
The North ◽  
Meridional Overturning ◽  
The Relationship ◽  
D Model

Abstract. A two dimensional scavenging-circulation model is used to investigate the patterns of sediment 231Pa/230Th generated by the Atlantic Meridional Overturning Circulation (AMOC) and further advance the application of this proxy for ocean paleocirculation studies. The scavenging parameters and the geometry of the overturning circulation cell have been chosen so that the model generates meridional sections of dissolved 230Th and 231Pa consistent with published water column profiles and an additional 12 previously unpublished profiles measured in the North and Equatorial Atlantic. The processes that generate the meridional sections of dissolved and particulate 230Th, dissolved and particulate 231Pa, dissolved and particulate 231Pa/230Th, and sediment 231Pa/230Th are discussed in detail. The results indicate that the relationship between sediment 231Pa/230Th at any given site and the overturning circulation is very complex. They clearly show that constraining past changes in the strength and geometry of the AMOC requires an extensive data set and they suggest strategies to maximize information from a limited number of samples.

scholarly journals Modeling a modern-like <i>p</i>CO<sub>2</sub> warm period (Marine Isotope Stage KM5c) with two versions of an Institut Pierre Simon Laplace atmosphere–ocean coupled general circulation model

2020 ◽  
Vol 16 (1) ◽  
pp. 1-16 ◽  
Author(s):  
Ning Tan ◽  
Camille Contoux ◽  
Gilles Ramstein ◽  
Yong Sun ◽  
Christophe Dumas ◽  
...  
Keyword(s):  
General Circulation Model ◽  
High Latitude ◽  
General Circulation ◽  
Greenland Ice Sheet ◽  
Circulation Model ◽  
Warm Period ◽  
Meridional Overturning Circulation ◽  
Marine Isotope Stage ◽  
Warm Climate ◽  
Coupled General Circulation Model

Abstract. The mid-Piacenzian warm period (3.264 to 3.025 Ma) is the most recent geological period with present-like atmospheric pCO2 and is thus expected to have exhibited a warm climate similar to or warmer than the present day. On the basis of understanding that has been gathered on the climate variability of this interval, a specific interglacial (Marine Isotope Stage KM5c, MIS KM5c; 3.205 Ma) has been selected for the Pliocene Model Intercomparison Project phase 2 (PlioMIP 2). We carried out a series of experiments according to the design of PlioMIP2 with two versions of the Institut Pierre Simon Laplace (IPSL) atmosphere–ocean coupled general circulation model (AOGCM): IPSL-CM5A and IPSL-CM5A2. Compared to the PlioMIP 1 experiment, run with IPSL-CM5A, our results show that the simulated MIS KM5c climate presents enhanced warming in mid- to high latitudes, especially over oceanic regions. This warming can be largely attributed to the enhanced Atlantic Meridional Overturning Circulation caused by the high-latitude seaway changes. The sensitivity experiments, conducted with IPSL-CM5A2, show that besides the increased pCO2, both modified orography and reduced ice sheets contribute substantially to mid- to high latitude warming in MIS KM5c. When considering the pCO2 uncertainties (+/-50 ppmv) during the Pliocene, the response of the modeled mean annual surface air temperature to changes to pCO2 (+/-50 ppmv) is not symmetric, which is likely due to the nonlinear response of the cryosphere (snow cover and sea ice extent). By analyzing the Greenland Ice Sheet surface mass balance, we also demonstrate its vulnerability under both MIS KM5c and modern warm climate.

Sign in / Sign up

Export Citation Format

Share Document