How do high-latitude North Atlantic climate signals the crossover between the Deep Western Boundary Current and the Gulf Stream?

2003 ◽  
Vol 30 (2) ◽  
Author(s):  
Jiayan Yang ◽  
Terrence M. Joyce
Keyword(s):  
North Atlantic ◽  
High Latitude ◽  
Gulf Stream ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Deep Western Boundary Current ◽  
North Atlantic Climate ◽  
Climate Signals

The Deep Western Boundary Current and Adjacent Interior Circulation at 24°–30°N: Mean Structure and Mesoscale Variability

2020 ◽  
Vol 50 (9) ◽  
pp. 2735-2758
Author(s):  
Tiago Carrilho Biló ◽  
William E. Johns
Keyword(s):  
North Atlantic ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Deep Western Boundary Current ◽  
Mean Structure ◽  
The Mean ◽  
Theoretical Evidence ◽  
Anticyclonic Eddies ◽  
Geostrophic Velocities

AbstractThe mean North Atlantic Deep Water (NADW, 1000 < z < 5000 m) circulation and deep western boundary current (DWBC) variability offshore of Abaco, Bahamas, at 26.5°N are investigated from nearly two decades of velocity and hydrographic observations, and outputs from a 30-yr-long eddy-resolving global simulation. Observations at 26.5°N and Argo-derived geostrophic velocities show the presence of a mean Abaco Gyre spanning the NADW layer, consisting of a closed cyclonic circulation between approximately 24° and 30°N and 72° and 77°W. The southward-flowing portion of this gyre (the DWBC) is constrained to within ~150 km of the western boundary with a mean transport of ~30 Sv (1 Sv ≡ 106 m3 s−1). Offshore of the DWBC, the data show a consistent northward recirculation with net transports varying from 6.5 to 16 Sv. Current meter records spanning 2008–17 supported by the numerical simulation indicate that the DWBC transport variability is dominated by two distinct types of fluctuations: 1) periods of 250–280 days that occur regularly throughout the time series and 2) energetic oscillations with periods between 400 and 700 days that occur sporadically every 5–6 years and force the DWBC to meander far offshore for several months. The shorter-period variations are related to DWBC meandering caused by eddies propagating southward along the continental slope at 24°–30°N, while the longer-period oscillations appear to be related to large anticyclonic eddies that slowly propagate northwestward counter to the DWBC flow between ~20° and 26.5°N. Observational and theoretical evidence suggest that these two types of variability might be generated, respectively, by DWBC instability processes and Rossby waves reflecting from the western boundary.

Dynamics of Deep Recirculation Cells Offshore of the Deep Western Boundary Current in the Subtropical North Atlantic (15°–30°N)

2021 ◽  
Vol 51 (1) ◽  
pp. 131-145
Author(s):  
Tiago Carrilho Biló ◽  
William E Johns ◽  
Jian Zhao
Keyword(s):  
North Atlantic ◽  
Primary Source ◽  
Water Layer ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Study Region ◽  
Deep Western Boundary Current ◽  
Deep Water Layer ◽  
Circulation Patterns

AbstractThe dynamics of the deep recirculation offshore of the deep western boundary current (DWBC) between 15° and 30°N within the upper North Atlantic Deep Water layer (1000 ≤ z ≤ 3000 m) is investigated with two different eddy-resolving numerical simulations. Despite some differences in the recirculation cells, our assessment of the modeled deep isopycnal circulation patterns (36.77 ≤ σ2 ≤ 37.06 kg m−3) shows that both simulations predict the DWBC flowing southward along the continental slope, while the so-called Abaco Gyre and two additional cyclonic cells recirculate waters northward in the interior. These cells are a few degrees wide, located along the DWBC path, and characterized by potential vorticity (PV) changes occurring along their mean streamlines. The analysis of the mean PV budget reveals that these changes result from the action of eddy forcing that tends to erode the PV horizontal gradients. The lack of a major upper-ocean boundary current within the study region, and the fact that the strongest eddy forcing is constrained within a few hundreds of kilometers of the western boundary, suggest that the DWBC is the primary source of eddy forcing. Finally, the eddies responsible for forcing the recirculation have dominant time scales between 100 and 300 days, which correspond to the primary observed variability scales of the DWBC transport at 26.5°N.

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