On the calculation of wind stress curl over open ocean areas from synoptic meteorological data with application to time dependent ocean circulation

Abstract A new framework is proposed for investigating the atmospheric forcing of North Atlantic Ocean circulation. Instead of using classical modes of variability, such as the North Atlantic Oscillation (NAO) or the east Atlantic pattern, the weather regimes paradigm was used. Using this framework helped avoid problems associated with the assumptions of orthogonality and symmetry that are particular to modal analysis and known to be unsuitable for the NAO. Using ocean-only historical and sensitivity experiments, the impacts of the four winter weather regimes on horizontal and overturning circulations were investigated. The results suggest that the Atlantic Ridge (AR), negative NAO (NAO−), and positive NAO (NAO+) regimes induce a fast (monthly-to-interannual time scales) adjustment of the gyres via topographic Sverdrup dynamics and of the meridional overturning circulation via anomalous Ekman transport. The wind anomalies associated with the Scandinavian blocking regime (SBL) are ineffective in driving a fast wind-driven oceanic adjustment. The response of both gyre and overturning circulations to persistent regime conditions was also estimated. AR causes a strong, wind-driven reduction in the strengths of the subtropical and subpolar gyres, while NAO+ causes a strengthening of the subtropical gyre via wind stress curl anomalies and of the subpolar gyre via heat flux anomalies. NAO− induces a southward shift of the gyres through the southward displacement of the wind stress curl. The SBL is found to impact the subpolar gyre only via anomalous heat fluxes. The overturning circulation is shown to spin up following persistent SBL and NAO+ and to spin down following persistent AR and NAO− conditions. These responses are driven by changes in deep water formation in the Labrador Sea.

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Evaluation of CMIP3 and CMIP5 Wind Stress Climatology Using Satellite Measurements and Atmospheric Reanalysis Products

Journal of Climate ◽

10.1175/jcli-d-12-00591.1 ◽

2013 ◽

Vol 26 (16) ◽

pp. 5810-5826 ◽

Cited By ~ 46

Author(s):

Tong Lee ◽

Duane E. Waliser ◽

Jui-Lin F. Li ◽

Felix W. Landerer ◽

Michelle M. Gierach

Keyword(s):

Climate Variability ◽

Wind Stress ◽

Ocean Circulation ◽

Zonal Wind ◽

Global Ocean ◽

Equatorial Pacific Ocean ◽

Equatorial Atlantic ◽

Wind Stress Curl ◽

Meridional Heat Transport ◽

Easterly Wind

Abstract Wind stress measurements from the Quick Scatterometer (QuikSCAT) satellite and two atmospheric reanalysis products are used to evaluate the annual mean and seasonal cycle of wind stress simulated by phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5). The ensemble CMIP3 and CMIP5 wind stresses are very similar to each other. Generally speaking, there is no significant improvement of CMIP5 over CMIP3. The CMIP ensemble–average zonal wind stress has eastward biases at midlatitude westerly wind regions (30°–50°N and 30°–50°S, with CMIP being too strong by as much as 55%), westward biases in subtropical–tropical easterly wind regions (15°–25°N and 15°–25°S), and westward biases at high-latitude regions (poleward of 55°S and 55°N). These biases correspond to too strong anticyclonic (cyclonic) wind stress curl over the subtropical (subpolar) ocean gyres, which would strengthen these gyres and influence oceanic meridional heat transport. In the equatorial zone, significant biases of CMIP wind exist in individual basins. In the equatorial Atlantic and Indian Oceans, CMIP ensemble zonal wind stresses are too weak and result in too small of an east–west gradient of sea level. In the equatorial Pacific Ocean, CMIP zonal wind stresses are too weak in the central and too strong in the western Pacific. These biases have important implications for the simulation of various modes of climate variability originating in the tropics. The CMIP as a whole overestimate the magnitude of seasonal variability by almost 50% when averaged over the entire global ocean. The biased wind stress climatologies in CMIP not only have implications for the simulated ocean circulation and climate variability but other air–sea fluxes as well.

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On the connection between coastal Ekman upwelling and wind-stress-curl-driven upwelling off the southwest African coasts

10.5194/egusphere-egu21-12206 ◽

2021 ◽

Author(s):

Mohammad Hadi Bordbar ◽

Volker Mohrholz ◽

Martin Schmidt

Keyword(s):

Chlorophyll A ◽

Wind Stress ◽

Coastal Upwelling ◽

Model Simulation ◽

Marine Ecosystem ◽

Phase Relationship ◽

Open Ocean ◽

Wind Stress Curl ◽

Upwelled Water ◽

Ekman Theory

<p>Spatial and temporal variations of nutrient-rich upwelled water across the major eastern boundary upwelling systems are primarily controlled by the surface atmospheric flow with different, and sometimes contrasting, impacts on coastal and open-ocean upwelling systems. Here, concurrently measured wind-fields, satellite-derived Chlorophyll-a concentration along with a state-of-the-art ocean model simulation spanning 2008-2018 are used to investigate the connection between coastal and offshore physical drivers of the Benguela Upwelling System (BUS). Our results indicate that the spatial structure of long-term mean upwelling derived from Ekman theory and the numerical model are fairly consistent across the entire BUS and closely followed by the Chlorophyll-a pattern. The variability of the upwelling from the Ekman theory is proportionally diminished with offshore distance, whereas different and sometimes opposite structures are revealed in the model-derived upwelling. Our result suggests the presence of sub-mesoscale activity (i.e. filaments and eddies) across the entire BUS with a large modulating effect on the wind-stress-curl-driven upwelling off L&#252;deritz and Walvis Bay. In Kunene and Cape Frio upwelling cells, located in the northern sector of the BUS, the coastal upwelling and open-ocean upwelling frequently alternate each other, whereas they are modulated by the annual cycle and mostly in phase off Walvis Bay. Such a phase relationship appears to be strongly seasonal dependent off L&#252;deritz and across the southern BUS. Thus, our findings suggest this relationship is far more complex than currently thought and seems to be sensitive to climate changes with short- and far-reaching consequences for this vulnerable marine-ecosystem.</p>

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Multidecadal simulation of the tropical and subtropical South Atlantic Ocean with a high resolution ocean model forced by ERA-5 reanalysis data

10.5194/egusphere-egu2020-21190 ◽

2020 ◽

Author(s):

Martin Schmidt ◽

Hadi Bordbar ◽

Fernanda Nascimento ◽

Claudia Frauen

Keyword(s):

High Resolution ◽

Wind Stress ◽

Ocean Circulation ◽

Reanalysis Data ◽

Ocean Model ◽

Ecosystem Dynamics ◽

Boundary Current ◽

Wind Stress Curl ◽

Data Set ◽

Upwelling Intensity

<p>High resolution regional ocean circulation models are needed to investigate regional ecosystem dynamics. However, these models may suffer from biases due to shortcomings in reanalysis datasets like NCEP or ERA-Interin, that have traditionally been used as atmospheric forcing. More realistic results can be achieved by replacing the reanalysed wind with scatterometer based winds. However, inconsistencies between different scatterometers like ASCAT and QuikSCAT introduce new uncertainty, which prevents a discussion of long-term trends in these models. The ERA-5 reanalysis offers a new consistent data set to force highly resolving regional ocean models. Based on such a simulation we analyse trends and anomalies in poleward currents in the Eastern Boundary Current off Southern Africa and Northern Benguela upwelling intensity due to changing wind stress and wind stress curl. Model results are validated with remote sensing as well as shipborne and mooring data. Further, variability of oxygen conditions in the Northern Benguela and the Angola Gyre oxygen minimum zone is discussed.&#160;</p>

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The Influence of Longitudinal Variations in Wind Stress Curl on the Steady Ocean Circulation

Journal of Physical Oceanography ◽

10.1175/1520-0485(1975)005<0334:tiolvi>2.0.co;2 ◽

1975 ◽

Vol 5 (2) ◽

pp. 334-346 ◽

Cited By ~ 10

Author(s):

Kern E. Kenyon

Keyword(s):

Wind Stress ◽

Ocean Circulation ◽

Wind Stress Curl ◽

Longitudinal Variations

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Stochastic Forcing of the North Atlantic Wind-Driven Ocean Circulation. Part II: An Analysis of the Dynamical Ocean Response Using Generalized Stability Theory

Journal of Physical Oceanography ◽

10.1175/jpo2853.1 ◽

2006 ◽

Vol 36 (3) ◽

pp. 316-334 ◽

Cited By ~ 5

Author(s):

Kettyah C. Chhak ◽

Andrew M. Moore ◽

Ralph F. Milliff ◽

Grant Branstator ◽

William R. Holland ◽

...

Keyword(s):

Wind Stress ◽

Ocean Circulation ◽

North Atlantic ◽

Boundary Region ◽

Western Boundary ◽

Transient Growth ◽

Wind Stress Curl ◽

Stochastic Forcing ◽

The North ◽

The North Atlantic

Abstract As discussed in Part I of this study, the magnitude of the stochastic component of wind stress forcing is comparable to that of the seasonal cycle and thus will likely have a significant influence on the ocean circulation. By forcing a quasigeostrophic model of the North Atlantic Ocean circulation with stochastic wind stress curl data from the NCAR CCM3, it was found in Part I that much of the stochastically induced variability in the ocean circulation is confined to the western boundary region and some major topographic features even though the stochastic forcing is basinwide. This can be attributed to effects of bathymetry and vorticity gradients in the basic state on the system eigenmodes. Using generalized stability theory (GST), it was found in Part I that transient growth due to the linear interference of nonnormal eigenmodes enhances the stochastically induced variance. In the present study, the GST analysis of Part I is extended and it is found that the patterns of wind stress curl that are most effective for inducing variability in the model have their largest projection on the most nonnormal eigenmodes of the system. These eigenmodes are confined primarily to the western boundary region and are composed of long Rossby wave packets that are Doppler shifted by the Gulf Stream to have eastward group velocity. Linear interference of these eigenmodes yields transient growth of stochastically induced perturbations, and it is this process that maintains the variance of the stochastically induced circulations. Analysis of the large-scale circulation also reveals that the system possesses a large number of degrees of freedom, which has significant implications for ocean prediction. Sensitivity studies show that the results and conclusions of this study are insensitive and robust to variations in model parameters and model configuration.

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On the theory of the wind-driven ocean circulation

Journal of Fluid Mechanics ◽

10.1017/s0022112062000038 ◽

1962 ◽

Vol 12 (1) ◽

pp. 49-80 ◽

Cited By ~ 46

Author(s):

G. F. Carrier ◽

A. R. Robinson

Keyword(s):

Wind Stress ◽

Ocean Circulation ◽

Surface Wind ◽

Inviscid Flow ◽

Relative Vorticity ◽

Wind Stress Curl ◽

Meridional Transport ◽

Surface Distribution ◽

Surface Wind Stress ◽

Mean Circulation

A surface distribution of stress is imposed on an ocean enclosed by two continental boundaries; the resulting transport circulation is studied between two latitudes of zero surface wind-stress curl, within which the curl reaches a single maximum. Under the assumption that turbulent transfer of relative vorticity has a minimum effect on the mean circulation, inviscid flow patterns are deduced in the limit of small transport Rossby number. Inertial currents, or naturally scaled regions of high relative vorticity, occur on both the eastern and the western continental coasts. Limits on the relative transports of the currents are obtained and found to depend on the direction of variation of the wind-stress curl with latitude, relative to that of the Coriolis accelerations. The most striking feature of the inviscid flow is a narrow inertial current the axis of which lies along the latitude of maximum wind-stress curl. All eastward flow occurs in this midlatitude jet.A feature of the flow which cannot remain essentially free of turbulent processes is the integrated vorticity relationship, since the imposed wind-stress distribution acts as a net source of vorticity for the ocean. Heuristic arguments are used together with this integral constraint to deduce the presence and strength of the turbulent diffusion which must occur in the region of the mid-latitude jet. It is further inferred that the turbulent meanders of the jet must effect a net meridional transport of relative vorticity.

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Mesoscale and wind-driven intra-annual variability in the East Auckland Current

Scientific Reports ◽

10.1038/s41598-021-89222-3 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Rafael Santana ◽

Sutara H. Suanda ◽

Helen Macdonald ◽

Joanne O’Callaghan

Keyword(s):

Continental Shelf ◽

Continental Slope ◽

Wind Stress ◽

Ocean Circulation ◽

Shelf Break ◽

Ekman Transport ◽

Wind Stress Curl ◽

Annual Variability ◽

Continental Shelf Break

AbstractIntra-annual variability in the East Auckland Current (EAuC) was studied using a year-long timeseries of in situ and remotely-sensed velocity, temperature and salinity observations. Satellite-derived velocities correlated well ($$\hbox {r} > 0.75$$ r > 0.75 ) with in situ observations and well-represent the long-term ($$> 30$$ > 30 days) variability of the upper ocean circulation. Four mesoscale eddies were observed during the year (for 260 days) which generated distinct flows between the continental slope and rise. The EAuC dominated the circulation in the continental shelf break, slope and rise for 110 days and generated the most energetic events associated with wind forcing. Current variability on the continental slope was coherent with along-slope wind stress (wind stress curl) at periods between 4 and 12 days (16 and 32 days). We suggest that along-slope winds generated offshore Ekman transport, uplift on the shelf-break, and a downwind geostrophic jet on the slope. In contrast, positive wind stress curl caused convergence of water, downwelling, and increased the current speed in the region. Bottom Ekman transport, generated by the EAuC, was suggested to have caused the largest temperature anomaly ($$-1.5 ^{\circ }\hbox {C}$$ - 1 . 5 ∘ C ) at the continental shelf-break.

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Mesoscale and Wind-Driven Variability in The East Auckland Current

10.21203/rs.3.rs-228104/v1 ◽

2021 ◽

Author(s):

Rafael Santana ◽

Sutara H. Suanda ◽

Helen Macdonald ◽

Joanne O’Callaghan

Keyword(s):

Continental Shelf ◽

Continental Slope ◽

Wind Stress ◽

Ocean Circulation ◽

Shelf Break ◽

Ekman Transport ◽

Wind Stress Curl ◽

Slope Winds ◽

Continental Shelf Break

Abstract East Auckland Current (EAuC) variability was studied using a year-long timeseries of in situ and remotely-sensed velocity, temperature and salinity observations. Satellite-derived velocities correlated well (r > 0.75) with in situ observations and well-represent the long-term (> 30 day) variability of the upper ocean circulation. Four mesoscale eddies were observed during the year (for 260 days) which generated distinct flows between the continental slope and rise. The EAuC dominated the circulation in the continental shelf break, slope and rise for 110 days and generated the most energetic events associated with wind forcing. Current variability on the continental slope was coherent with along-slope wind stress (wind stress curl) at periods between 4 and 12 days (16 and 32 days). We suggest that along-slope winds generated offshore Ekman transport, uplift on the shelf-break, and a downwind geostrophic jet on the slope. In contrast, positive wind stress curl caused convergence of water, downwelling, and increased the current speed in the region. Bottom Ekman transport, generated by the EAuC, was suggested to have caused the largest temperature anomaly (-1.5°C) at the continental shelf-break.

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Simulation of north India Ocean circulation Using a simple barotropic model and Some sensitivity studies

MAUSAM ◽

10.54302/mausam.v43i4.3501 ◽

2021 ◽

Vol 43 (4) ◽

pp. 353-360

Author(s):

S. K. BEHERA ◽

H. J. SAWANT ◽

P. S. SALVEKAR

Keyword(s):

Indian Ocean ◽

Wind Stress ◽

Ocean Circulation ◽

North Indian Ocean ◽

North India ◽

Wind Stress Curl ◽

Meridional Component ◽

Barotropic Model ◽

The North ◽

Sensitivity Studies

A non-divergent barotropic model has been formulated on the basis of splitting up method and used to study the circulation in the north Indian Ocean (1-26° N, 4~-99° E). The circulation was simulated for summer and winter seasons separately. It IS found that the model simulated the summer and winter calculation satisfactorily. It is also found that the meridional component of wind stress IS dominant over the zonal component in shaping the Somali current. Some sensitivity studies were also carried out and the results indicate the importance of wind stress curl.

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