Mesoscale motions near the deep western boundary of the North Atlantic

1978 ◽  
Vol 25 (12) ◽  
pp. 1179-1191 ◽  
Author(s):  
Stephen C. Riser ◽  
Howard Freeland ◽  
H.Thomas Rossby
Keyword(s):  
North Atlantic ◽  
Western Boundary ◽  
The North ◽  
The North Atlantic

Identification and quantification of the North Atlantic Deep Water pathways

2021 ◽  
Author(s):  
Philippe Miron ◽  
Maria J. Olascoaga ◽  
Francisco J. Beron-Vera ◽  
Kimberly L. Drouin ◽  
M. Susan Lozier
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Sea Water ◽  
Lower Layer ◽  
North Atlantic Deep Water ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Western Boundary ◽  
The North ◽  
The North Atlantic

<p>The North Atlantic Deep Water (NADW) flows equatorward along the Deep Western Boundary Current (DWBC) as well as interior pathways and is a critical part of the Atlantic Meridional Overturning Circulation. Its upper layer, the Labrador Sea Water (LSW), is formed by open-ocean deep convection in the Labrador and Irminger Seas while its lower layers, the Iceland–Scotland Overflow Water (ISOW) and the Denmark Strait Overflow Water (DSOW), are formed north of the Greenland–Iceland–Scotland Ridge.</p><p>In recent years, more than two hundred acoustically-tracked subsurface floats have been deployed in the deep waters of the North Atlantic.  Studies to date have highlighted water mass pathways from launch locations, but due to limited float trajectory lengths, these studies have been unable to identify pathways connecting  remote regions.</p><p>This work presents a framework to explore deep water pathways from their respective sources in the North Atlantic using Markov Chain (MC) modeling and Transition Path Theory (TPT). Using observational trajectories released as part of OSNAP and the Argo projects, we constructed two MCs that approximate the lower and upper layers of the NADW Lagrangian dynamics. The reactive NADW pathways—directly connecting NADW sources with a target at 53°N—are obtained from these MCs using TPT.</p><p>Preliminary results show that twenty percent more pathways of the upper layer(LSW) reach the ocean interior compared to  the lower layer (ISOW, DSOW), which mostly flows along the DWBC in the subpolar North Atlantic. Also identified are the Labrador Sea recirculation pathways to the Irminger Sea and the direct connections from the Reykjanes Ridge to the eastern flank of the Mid–Atlantic Ridge, both previously observed. Furthermore, we quantified the eastern spread of the LSW to the area surrounding the Charlie–Gibbs Fracture Zone and compared it with previous analysis. Finally, the residence time of the upper and lower layers are assessed and compared to previous observations.</p>

Variability of the Meridional Overturning in the North Atlantic from the 50-Year GECCO State Estimation

2008 ◽  
Vol 38 (9) ◽  
pp. 1913-1930 ◽  
Author(s):  
Armin Köhl ◽  
Detlef Stammer
Keyword(s):  
Time Scales ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Meridional Overturning Circulation ◽  
Special Focus ◽  
Western Boundary ◽  
Consistent Estimate ◽  
The North ◽  
Meridional Overturning ◽  
The North Atlantic

Abstract The German partner of the consortium for Estimating the Circulation and Climate of the Ocean (GECCO) provided a dynamically consistent estimate of the time-varying ocean circulation over the 50-yr period 1952–2001. The GECCO synthesis combines most of the data available during the entire estimation period with the ECCO–Massachusetts Institute of Technology (MIT) ocean circulation model using its adjoint. This GECCO estimate is analyzed here for the period 1962–2001 with respect to decadal and longer-term changes of the meridional overturning circulation (MOC) of the North Atlantic. A special focus is on the maximum MOC values at 25°N. Over this period, the dynamically self-consistent synthesis stays within the error bars of H. L. Bryden et al., but reveals a general increase of the MOC strength. The variability on decadal and longer time scales is decomposed into contributions from different processes. Changes in the model’s MOC strength are strongly influenced by the southward communication of density anomalies along the western boundary originating from the subpolar North Atlantic, which are related to changes in the Denmark Strait overflow but are only marginally influenced by water mass formation in the Labrador Sea. The influence of density anomalies propagating along the southern edge of the subtropical gyre associated with baroclinically unstable Rossby waves is found to be equally important. Wind-driven processes such as local Ekman transport explain a smaller fraction of the variability on those long time scales.

scholarly journals Sensitivity of winter North Atlantic-European climate to resolved atmosphere and ocean dynamics

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Reindert J. Haarsma ◽  
Javier García-Serrano ◽  
Chloé Prodhomme ◽  
Omar Bellprat ◽  
Paolo Davini ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
North Atlantic ◽  
Gulf Stream ◽  
Ocean Dynamics ◽  
Small Scale ◽  
Western Boundary ◽  
The North ◽  
The North Atlantic ◽  
Mean Climate ◽  
Meso Scale

Abstract Northern Hemisphere western boundary currents, like the Gulf Stream, are key regions for cyclogenesis affecting large-scale atmospheric circulation. Recent observations and model simulations with high-temporal and -spatial resolution have provided evidence that the associated ocean fronts locally affect troposphere dynamics. A coherent view of how this affects the mean climate and its variability is, however, lacking. In particular the separate role of resolved ocean and atmosphere dynamics in shaping the atmospheric circulation is still largely unknown. Here we demonstrate for the first time, by using coupled seasonal forecast experiments at different resolutions, that resolving meso-scale oceanic variability in the Gulf Stream region strongly affects mid-latitude interannual atmospheric variability, including the North Atlantic Oscillation. Its impact on climatology, however, is minor. Increasing atmosphere resolution to meso-scale, on the other hand, strongly affects mean climate but moderately its variability. We also find that regional predictability relies on adequately resolving small-scale atmospheric processes, while resolving small-scale oceanic processes acts as an unpredictable source of noise, except for the North Atlantic storm-track where the forcing of the atmosphere translates into skillful predictions.

Fine spatial structure of the North Atlantic current's western boundary

1994 ◽  
Vol 5 (4) ◽  
pp. 279-285
Author(s):  
A. N. Paramonov ◽  
O. B. Zakharov ◽  
A. A. Metalnikov
Keyword(s):  
Spatial Structure ◽  
North Atlantic ◽  
Western Boundary ◽  
The North ◽  
The North Atlantic

scholarly journals A Model Analysis of the Behavior of the Mediterranean Water in the North Atlantic

2007 ◽  
Vol 37 (3) ◽  
pp. 764-786 ◽  
Author(s):  
Yanli Jia ◽  
Andrew C. Coward ◽  
Beverly A. de Cuevas ◽  
David J. Webb ◽  
Sybren S. Drijfhout
Keyword(s):  
North Atlantic ◽  
Current System ◽  
Global Ocean ◽  
Western Boundary ◽  
Depth Range ◽  
Strait Of Gibraltar ◽  
The North ◽  
The North Atlantic ◽  
The Mediterranean ◽  
Mediterranean Water

Abstract The behavior of the Mediterranean Water in the North Atlantic Ocean sector of a global ocean general circulation model is explored, starting from its entry point at the Strait of Gibraltar. The analysis focuses primarily on one experiment in which explicit watermass exchange between the Mediterranean Sea and the Atlantic at the Strait of Gibraltar is permitted. The model produces an exchange rate of approximately 1 Sv (Sv ≡ 106 m3 s−1). This is comparable to estimates derived from field measurements. The density of the Mediterranean outflow, however, is lower than observed, mainly because of its high temperature (more than 2°C higher than in reality). The lower density of the outflow and the model’s inadequate representation of the entrainment mixing in the outflow region cause the Mediterranean Water to settle in a depth range ∼800–1000 m in the North Atlantic, about 200 m shallower than observed. Here an interesting current system forms in response to the intrusion of the Mediterranean Water, involving three main pathways. In the first, the Mediterranean Water heads roughly westward across the basin and joins the deep western boundary current. In the second, the water travels northward along the eastern boundary reaching as far as Iceland, where it turns westward to participate in the deep circulation of the subpolar gyre. In the third, the water initially moves westward to the central Atlantic just north of 30°N before turning northwestward to reach an upwelling region at the Grand Banks off Newfoundland. At this location, the saline Mediterranean Water is drawn upward to the ocean upper layer and entrained into the North Atlantic Current system flowing to the northeastern basin; part of the current system enters the Nordic seas.

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