Structure and Variability of Meridional Overturning Circulation in the North Atlantic Subpolar Gyre in 2007–2017

2018 ◽  
Vol 483 (4) ◽  
pp. 437-441
Author(s):  
S. Gladyshev ◽  
◽  
V. Gladyshev ◽  
S. Gulev ◽  
A. Sokov ◽  
...  
Keyword(s):  
North Atlantic ◽  
Meridional Overturning Circulation ◽  
Subpolar Gyre ◽  
Overturning Circulation ◽  
The North ◽  
North Atlantic Subpolar Gyre ◽  
Meridional Overturning ◽  
The North Atlantic

scholarly journals Simultaneous Evolution of Gyre and Atlantic Meridional Overturning Circulation Anomalies as an Eigenmode of the North Atlantic System

2017 ◽  
Vol 30 (17) ◽  
pp. 6737-6755
Author(s):  
Bowen Zhao ◽  
Thomas Reichler ◽  
Courtenay Strong ◽  
Cecile Penland
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Half Cycle ◽  
Subpolar Gyre ◽  
Overturning Circulation ◽  
The North ◽  
Meridional Overturning ◽  
The North Atlantic

The authors identify an interdecadal oscillatory mode of the North Atlantic atmosphere–ocean system in a general circulation model (GFDL CM2.1) via a linear inverse model (LIM). The oscillation mechanism is mostly embedded in the subpolar gyre: anomalous advection generates density anomalies in the eastern subpolar gyre, which propagate along the mean gyre circulation and reach the subpolar gyre center around 10 years later, when associated anomalous advection of the opposite sign starts the other half cycle. As density anomalies reach the Labrador Sea deep convection region, Atlantic meridional overturning circulation (AMOC) anomalies are also induced. Both the gyre and AMOC anomalies then propagate equatorward slowly, following the advection of density anomalies. The oscillation is further demonstrated to be more likely an ocean-only mode while excited by the atmospheric forcing; in particular, it can be approximated as a linearly driven damped oscillator that is partly excited by the North Atlantic Oscillation (NAO). The slowly evolving interdecadal oscillation significantly improves and prolongs the LIM’s prediction skill of sea surface temperature (SST) evolution.

Subpolar Gyre – AMOC – Atmosphere Interactions on Multidecadal Timescales in a Version of the Kiel Climate Model

2021 ◽  
Author(s):  
Jing Sun ◽  
Mojib Latif ◽  
Wonsun Park
Keyword(s):  
North Atlantic ◽  
Climate Model ◽  
Deep Convection ◽  
Meridional Overturning Circulation ◽  
Subpolar Gyre ◽  
Surface Salinity ◽  
The North ◽  
Ocean Coupling ◽  
Meridional Overturning ◽  
The North Atlantic

<p>There is a controversy about the nature of multidecadal climate variability in the North Atlantic (NA) region, concerning the roles of ocean circulation and atmosphere-ocean coupling. Here we describe NA multidecadal variability from a version of the Kiel Climate Model, in which both subpolar gyre (SPG)-Atlantic Meridional Overturning Circulation (AMOC) and atmosphere-ocean coupling are essential. The oceanic barotropic streamfuntions, meridional overturning streamfunctions, and sea level pressure are jointly analyzed to derive the leading mode of Atlantic variability. This mode accounting for about 23.7 % of the total combined variance is oscillatory with an irregular periodicity of 25-50 years and an e-folding time of about a decade. SPG and AMOC mutually influence each other and together provide the delayed negative feedback necessary for maintaining the oscillation. An anomalously strong SPG, for example, drives higher surface salinity and density in the NA’s sinking region. In response, oceanic deep convection and AMOC intensify, which, with a time delay of about a decade, reduces SPG strength by enhancing upper-ocean heat content. The weaker gyre circulation leads to lower surface salinity and density in the sinking region, which eventually reduces deep convection and AMOC strength. There is a positive ocean-atmosphere feedback between the sea surface temperature and low-level atmospheric circulation over the Southern Greenland area, with related wind stress changes reinforcing SPG changes, thereby maintaining the (damped) multidecadal oscillation against dissipation. Stochastic surface heat-flux forcing associated with the North Atlantic Oscillation drives the eigenmode.</p>

scholarly journals Impact of Agulhas Leakage on the Atlantic Overturning Circulation in the CCSM4

2014 ◽  
Vol 27 (1) ◽  
pp. 101-110 ◽  
Author(s):  
Wilbert Weijer ◽  
Erik van Sebille
Keyword(s):  
North Atlantic ◽  
South Atlantic ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
Climate System Model ◽  
The North ◽  
Salinity Variability ◽  
Meridional Overturning ◽  
The North Atlantic ◽  
The Impact

Abstract The impact of Agulhas leakage variability on the strength of the Atlantic meridional overturning circulation (AMOC) in the Community Climate System Model, version 4 (CCSM4) is investigated. In this model an advective connection exists that transports salinity anomalies from the Agulhas region into the North Atlantic on decadal (30–40 yr) time scales. However, there is no identifiable impact of Agulhas leakage on the strength of the AMOC, suggesting that the salinity variations are too weak to significantly modify the stratification in the North Atlantic. It is argued that this study is inconclusive with respect to an impact of Agulhas leakage on the AMOC. Salinity biases leave the South Atlantic and Indian Oceans too homogeneous, in particular erasing the observed salinity front in the Agulhas retroflection region. Consequently, salinity variability in the southeastern South Atlantic is found to be much weaker than observed.

scholarly journals Impact of Labrador Sea Convection on the North Atlantic Meridional Overturning Circulation

2007 ◽  
Vol 37 (9) ◽  
pp. 2207-2227 ◽  
Author(s):  
Robert S. Pickart ◽  
Michael A. Spall
Keyword(s):  
North Atlantic ◽  
World Ocean ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Overturning Circulation ◽  
The North ◽  
Meridional Overturning ◽  
The North Atlantic ◽  
Density Space

Abstract The overturning and horizontal circulations of the Labrador Sea are deduced from a composite vertical section across the basin. The data come from the late-spring/early-summer occupations of the World Ocean Circulation Experiment (WOCE) AR7W line, during the years 1990–97. This time period was chosen because it corresponded to intense wintertime convection—the deepest and densest in the historical record—suggesting that the North Atlantic meridional overturning circulation (MOC) would be maximally impacted. The composite geostrophic velocity section was referenced using a mean lateral velocity profile from float data and then subsequently adjusted to balance mass. The analysis was done in depth space to determine the net sinking that results from convection and in density space to determine the diapycnal mass flux (i.e., the transformation of light water to Labrador Sea Water). The mean overturning cell is calculated to be 1 Sv (1 Sv ≡ 106 m3 s−1), as compared with a horizontal gyre of 18 Sv. The total water mass transformation is 2 Sv. These values are consistent with recent modeling results. The diagnosed heat flux of 37.6 TW is found to result predominantly from the horizontal circulation, both in depth space and density space. These results suggest that the North Atlantic MOC is not largely impacted by deep convection in the Labrador Sea.

Estimated Decadal Changes in the North Atlantic Meridional Overturning Circulation and Heat Flux 1993–2004

2006 ◽  
Vol 36 (11) ◽  
pp. 2012-2024 ◽  
Author(s):  
Carl Wunsch ◽  
Patrick Heimbach
Keyword(s):  
Heat Flux ◽  
Least Squares ◽  
North Atlantic ◽  
Meridional Overturning Circulation ◽  
Volume Flux ◽  
Overturning Circulation ◽  
The North ◽  
Least Squares Fit ◽  
Meridional Overturning ◽  
The North Atlantic

Abstract Results from a global 1° model constrained by least squares to a multiplicity of datasets over the interval 1992–2004 are used to describe apparent changes in the North Atlantic Ocean meridional overturning circulation and associated heat fluxes at 26°N. The least squares fit is both stable and adequately close to the data to make the analysis worthwhile. Changes over the 12 yr are spatially and temporally complex. A weak statistically significant trend is found in net North Atlantic volume flux above about 1200 m, which drops slightly (−0.19 ± 0.05 Sv yr−1; 1 Sv ≡ 106 m3 s−1) but with a corresponding strengthening of the outflow of North Atlantic Deep Water and inflow of abyssal waters. The slight associated trend in meridional heat flux is very small and not statistically significant. The month-to-month variability implies that single-section determinations of heat and volume flux are subject to serious aliasing errors.

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