Eddy variability east of Madagascar

2005 ◽  
Vol 363 (1826) ◽  
pp. 77-79 ◽  
Author(s):  
G. D. Quartly ◽  
J. J. H. Buck ◽  
M. A. Srokosz
Keyword(s):  
High Resolution ◽  
Numerical Model ◽  
East Coast ◽  
Sea Surface ◽  
Western Boundary ◽  
Biological Productivity ◽  
Boundary Current ◽  
Dynamic Height ◽  
Current Flows ◽  
Height Data

A strong but variable western boundary current flows south along the east coast of Madagascar, and at the island's southern end it interacts with eddies propagating zonally from the east. These two routes of variability are compared using altimetric sea–surface–height data and dynamic height from a high–resolution numerical model. The effects on biological productivity are also discussed.

scholarly journals Adjustment of the basin-scale circulation at 26° N to variations in Gulf Stream, deep western boundary current and Ekman transports as observed by the Rapid array

Ocean Science ◽  
2009 ◽  
Vol 5 (4) ◽  
pp. 421-433 ◽  
Author(s):  
H. L. Bryden ◽  
A. Mujahid ◽  
S. A. Cunningham ◽  
T. Kanzow
Keyword(s):  
Gulf Stream ◽  
Pressure Fluctuations ◽  
Western Boundary Current ◽  
Sea Surface ◽  
Western Boundary ◽  
Bottom Pressure ◽  
Boundary Current ◽  
Dynamic Height ◽  
Deep Western Boundary Current ◽  
Basin Scale

Abstract. The Rapid instrument array across the Atlantic Ocean along 26° N provides unprecedented monitoring of the basin-scale circulation. A unique feature of the Rapid array is the combination of full-depth moorings with instruments measuring temperature, salinity, pressure time series at many depths with co-located bottom pressure measurements so that dynamic pressure can be measured from surface to bottom. Bottom pressure measurements show a zonally uniform rise (and fall) of bottom pressure of 0.015 dbar on a 5 to 10 day time scale, suggesting that the Atlantic basin is filling and draining on a short time scale. After removing the zonally uniform bottom pressure fluctuations, bottom pressure variations at 4000 m depth against the western boundary compensate instantaneously for baroclinic fluctuations in the strength and structure of the deep western boundary current so there is no basin-scale mass imbalance resulting from variations in the deep western boundary current. After removing the mass compensating bottom pressure, residual bottom pressure fluctuations at the western boundary just east of the Bahamas balance variations in Gulf Stream transport. Again the compensation appears to be especially confined close to the western boundary. Thus, fluctuations in either Gulf Stream or deep western boundary current transports are compensated in a depth independent (barotropic) manner very close to the continental slope off the Bahamas. In contrast, compensation for variations in wind-driven surface Ekman transport appears to involve fluctuations in both western basin and eastern basin bottom pressures, though the bottom pressure difference fluctuations appear to be a factor of 3 too large, perhaps due to an inability to resolve small bottom pressure fluctuations after removal of larger zonal average, baroclinic, and Gulf Stream pressure components. For 4 tall moorings where time series dynamic height (geostrophic pressure) profiles can be estimated from sea surface to ocean bottom and bottom pressure can be added, there is no general correlation between surface dynamic height and bottom pressure. Dynamic height on each mooring is strongly correlated with sea surface height from satellite observations and the variability in both dynamic height and satellite sea surface height decrease sharply as the western boundary is approached.

scholarly journals THE BIFURCATION OF THE WESTERN BOUNDARY CURRENT SYSTEM OF THE SOUTH ATLANTIC OCEAN

2014 ◽  
Vol 32 (2) ◽  
pp. 241 ◽  
Author(s):  
Janini Pereira ◽  
Mariela Gabioux ◽  
Martinho Marta Almeida ◽  
Mauro Cirano ◽  
Afonso M. Paiva ◽  
...  
Keyword(s):  
High Resolution ◽  
Atlantic Ocean ◽  
Ocean Circulation ◽  
South Atlantic ◽  
Western Boundary Current ◽  
South Atlantic Ocean ◽  
Western Boundary ◽  
Intermediate Water ◽  
Boundary Current ◽  
The South

ABSTRACT. The results of two high-resolution ocean global circulation models – OGCMs (Hybrid Coordinate Ocean Model – HYCOM and Ocean Circulation andClimate Advanced Modeling Project – OCCAM) are analyzed with a focus on the Western Boundary Current (WBC) system of the South Atlantic Ocean. The volumetransports are calculated for different isopycnal ranges, which represent the most important water masses present in this region. The latitude of bifurcation of the zonalflows reaching the coast, which leads to the formation of southward or northward WBC flow at different depths (or isopycnal levels) is evaluated. For the Tropical Water,bifurcation of the South Equatorial Current occurs at 13◦-15◦S, giving rise to the Brazil Current, for the South Atlantic Central Water this process occurs at 22◦S.For the Antarctic Intermediate Water, bifurcation occurs near 28◦-30◦S, giving rise to a baroclinic unstable WBC at lower latitudes with a very strong vertical shearat mid-depths. Both models give similar results that are also consistent with previous observational studies. Observations of the South Atlantic WBC system havepreviously been sparse, consequently these two independent simulations which are based on realistic high-resolution OGCMs, add confidence to the values presentedin the literature regarding flow bifurcations at the Brazilian coast.Keywords: Southwestern Atlantic circulation, water mass, OCCAM, HYCOM. RESUMO. Resultados de dois modelos globais de alta resolução (HYCOM e OCCAM) são analisados focando o sistema de Corrente de Contorno Oeste do Oceano Atlântico Sul. Os transportes de volume são calculados para diferentes níveis isopicnais que representam as principais massas de água da região. É apresentada a avaliação da latitude de bifurcação do fluxo zonal que atinge a costa, permitindo a formação dos fluxos da Corrente de Contorno Oeste para o sul e para o norte emdiferentes níveis de profundidades (ou isopicnal). Para a Água Tropical, a bifurcação da Corrente Sul Equatorial ocorre entre 13◦-15◦S, originando a Corrente do Brasil, e para a Água Central do Atlântico Sul ocorre em 22◦S. A bifurcação daÁgua Intermediária Antártica ocorre próximo de 28◦-30◦S, dando um aumento na instabilidade baroclínica da Corrente de Contorno Oeste em baixas latitudes e com um forte cisalhamento vertical em profundidades intermediárias. Ambos os modelos apresentamresultados similares e consistentes com estudos observacionais prévios. Considerando que as observações do sistema de Corrente de Contorno Oeste do Atlântico Sul são escassas, essas duas simulações independentes com modelos globais de alta resolução adicionam confiança aos valores apresentados na literatura, relacionadosaos fluxos das bifurcações na costa do Brasil.Palavras-chave: circulação do Atlântico Sudoeste, massas de água, OCCAM, HYCOM.

scholarly journals The INALT family – a set of high-resolution nests for the Agulhas Current system within global NEMO ocean/sea-ice configurations

2019 ◽  
Vol 12 (7) ◽  
pp. 3329-3355 ◽  
Author(s):  
Franziska U. Schwarzkopf ◽  
Arne Biastoch ◽  
Claus W. Böning ◽  
Jérôme Chanut ◽  
Jonathan V. Durgadoo ◽  
...  
Keyword(s):  
High Resolution ◽  
Boundary Conditions ◽  
Current System ◽  
Western Boundary Current ◽  
Global Ocean ◽  
Western Boundary ◽  
Boundary Current ◽  
The South ◽  
Agulhas Current ◽  
Mesoscale Dynamics

Abstract. The Agulhas Current, the western boundary current of the South Indian Ocean, has been shown to play an important role in the connectivity between the Indian and Atlantic oceans. The greater Agulhas Current system is highly dominated by mesoscale dynamics. To investigate their influence on the regional and global circulations, a family of high-resolution ocean general circulation model configurations based on the NEMO code has been developed. Horizontal resolution refinement is achieved by embedding “nests” covering the South Atlantic and the western Indian oceans at 1/10∘ (INALT10) and 1/20∘ (INALT20) within global hosts with coarser resolutions. Nests and hosts are connected through two-way interaction, allowing the nests not only to receive boundary conditions from their respective host but also to feed back the impact of regional dynamics onto the global ocean. A double-nested configuration at 1/60∘ resolution (INALT60) has been developed to gain insights into submesoscale processes within the Agulhas Current system. Large-scale measures such as the Drake Passage transport and the strength of the Atlantic meridional overturning circulation are rather robust among the different configurations, indicating the important role of the hosts in providing a consistent embedment of the regionally refined grids into the global circulation. The dynamics of the Agulhas Current system strongly depend on the representation of mesoscale processes. Both the southward-flowing Agulhas Current and the northward-flowing Agulhas Undercurrent increase in strength with increasing resolution towards more realistic values, which suggests the importance of improving mesoscale dynamics as well as bathymetric slopes along this narrow western boundary current regime. The exploration of numerical choices such as lateral boundary conditions and details of the implementation of surface wind stress forcing demonstrates the range of solutions within any given configuration.

scholarly journals The historical development of physical research on the oceans bordering Southern Africa

1982 ◽  
Vol 1 (1) ◽  
pp. 42-52 ◽  
Author(s):  
J. R. E. Lutjeharms
Keyword(s):  
Ocean Circulation ◽  
Southern Africa ◽  
East Coast ◽  
Phenomenological Research ◽  
Historical Research ◽  
Western Boundary ◽  
Boundary Current ◽  
The West ◽  
Publication Rates ◽  
Circulation Patterns

Two archetypal ocean circulation patterns occur in the oceanic areas adjacent to southern Africa, namely, a western boundary current on the east coast and upwelling on the west coast. Investigation on the physical behaviour of these systems has passed through phases of exploratory, descriptive and phenomenological research. These historical research patterns are described briefly using mostly the publication rates on the physical oceanology of the areas in question.

Variability and meandering of the East Australian Current jet at 27oS

2021 ◽  
Author(s):  
Bernadette Sloyan ◽  
Christopher Chapman ◽  
Rebecca Cowley ◽  
Thomas Moore
Keyword(s):  
Continental Shelf ◽  
South Pacific ◽  
Sea Surface ◽  
Western Boundary ◽  
East Australian Current ◽  
Boundary Current ◽  
The South ◽  
Buoyancy Forcing ◽  
The Mean ◽  
Southward Flow

<p>The East Australian Current (EAC) is the complex and highly energetic western boundary current of the South Pacific Ocean gyre. Low frequency (>2 year) variability of the EAC reflects the changes in the wind and buoyancy forcing over the South Pacific. However, local and regional wind and buoyancy forcing drives higher frequency variability (< 1-2 year) of the EAC. Due to the narrow shelf, the EAC-jet  meandering has an immediate impact on the continental shelf circulation. Here we use the IMOS EAC mooring array between May 2015 to September 2019 and satellite observational data to quantify the quantify the EAC variability and assess the potential drives and impact of the on-shelf meandering of the EAC jet on the properties of the Coral and Tasman Seas.</p><p> </p><p>We find that there is considerable variability of Sea Surface Height (SSH) and Sea Surface temperature (SST) that at times co-vary, but at  other times the anomalies are opposed. We compare the surface anomalies with the EAC velocity and transport timeseries. The mean along-slope velocity vectors show poleward velocity dominates from 0-1500 m at the five mooring locations from the 500 m isobath to the deep abyssal basin with the strongest southward flow at the continental shelf. The variance ellipses show that the largest variability in EAC transport is in the along-shore direction. This indicates that the EAC variability is dominated by the movement of the EAC on- and off-shore. The EAC thus maintains its jet structure as it meanders onshore and offshore adjacent to the continental slope. While the mean along-shore velocity vectors provide a picture of the mean EAC, the time-series shows that the EAC has a complex and highly variable structure. Strong southward flow is associated with off-shore flow (positive across-slope velocity). While mostly measuring the EAC core we see times where the flow is northward (positive along-slope velocity). This northward velocity is due to the shelf flow extending from the coast to the shelf, and is generally associated with on-shore flow (negative across-slope velocity). These changes in the direction and strength of the velocity are driven by cyclonic eddies inshore of the jet, and have significant influence on the exchange between the open and shelf ocean.</p>

scholarly journals Malvinas-slope water intrusions on the northern Patagonia continental shelf

Ocean Science ◽  
2010 ◽  
Vol 6 (1) ◽  
pp. 345-359 ◽  
Author(s):  
A. R. Piola ◽  
N. Martínez Avellaneda ◽  
R. A. Guerrero ◽  
F. P. Jardón ◽  
E. D. Palma ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Continental Shelf ◽  
Sea Surface Temperature ◽  
Chlorophyll A ◽  
Local Development ◽  
Drake Passage ◽  
Negative Temperature ◽  
Sea Surface ◽  
Western Boundary ◽  
Boundary Current

Abstract. The Patagonia continental shelf located off southeastern South America is bounded offshore by the Malvinas Current, which extends northward from northern Drake Passage (~55° S) to nearly 38° S. The transition between relatively warm-fresh shelf waters and Subantarctic Waters from the western boundary current is characterized by a thermohaline front extending nearly 2500 km. We use satellite derived sea surface temperature, and chlorophyll-a data combined with hydrographic and surface drifter data to document the intrusions of slope waters onto the continental shelf near 41° S. These intrusions create vertically coherent localized negative temperature and positive salinity anomalies extending onshore about 150 km from the shelf break. The region is associated with a center of action of the first mode of non-seasonal sea surface temperature variability and also relatively high chlorophyll-a variability, suggesting that the intrusions are important in promoting the local development of phytoplankton. The generation of slope water penetrations at this location may be triggered by the inshore excursion of the 100 m isobath, which appears to steer the Malvinas Current waters over the outer shelf.

Extreme ocean weather induced by upstream meandering of the East Australian Current 

2021 ◽  
Author(s):  
Christopher Chapman ◽  
Bernadette Sloyan ◽  
Madeleine Cahill
Keyword(s):  
East Coast ◽  
Complex Dynamics ◽  
Heat Waves ◽  
Small Scale ◽  
Western Boundary ◽  
East Australian Current ◽  
Boundary Current ◽  
Atmospheric Blocking ◽  
Australian Continent ◽  
Current Region

<p>We investigate Marine Heat Waves and Marine Cold Spells (MHWs/MCSs) along the east coast of the Australian continent, a western boundary current region with exceedingly complex dynamics. We provide evidence that episodic MWHs/MCSs along the south-east of the Australian continent are driven by upstream variations in the position, but not necessarily the strength, of the East Australian Current, and that these variations are, in turn, controlled by small-scale (100s of kilometers) eddies that propagate into the region from the east. These eddies are able to alternately 'shut-off' and `turn-on' the poleward transport of warm water by the boundary current in a manner analogous to atmospheric blocking. Precursors to these `blocks' are detectable as much as 60 days prior to the onset of an event. We will discuss the implications of our results for the early prediction of MHW/MCS events.</p>

PREDICTION OF THE MOTION OF OIL SPILLS IN CANADIAN ARCTIC WATERS

1979 ◽  
Vol 1979 (1) ◽  
pp. 677-683 ◽  
Author(s):  
S. Venkatesh ◽  
H. S. Sahota ◽  
A. S. Rizkalla
Keyword(s):  
High Resolution ◽  
East Coast ◽  
Oil Spills ◽  
Surface Wind ◽  
Canadian Arctic ◽  
Sea Surface ◽  
Bay Of Fundy ◽  
Simulation Experiments ◽  
Water Currents ◽  
Environmental Prediction

ABSTRACT An oil spill movement prediction model operating as part of a real-time Environmental Prediction Support System for the Canadian Beaufort Sea has been developed. The present version of the model considers spills only in open waters, that is, the sea surface is considered to be ice free. The model has been partially verified with data obtained from oil simulation experiments conducted in the Bay of Fundy, off the east coast of Canada during the months of August and September, 1978. With the use of observed winds, the model-predicted locations of “Orion” buoys used to simulate the motion of oil on water, agreed fairly well with their observed locations. These verification tests also pointed out the need for high resolution surface wind forecasts — essential data for computing wind-driven water currents which move the oil.

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