Historical surface marine wind reports have been processed to define characteristic seasonal distributions of wind-stress curl over the four major eastern boundary current regions of the World Ocean (i.e., the California, Canary, Benguela, and Peru/Humboldt systems) on smaller scales than previously available. Interregional comparisons show that these “classical” coastal upwelling systems are characterized by cyclonic wind-stress curl near the continental boundaries and anticyclonic curl offshore, in association with predominantly equatorward (upwelling favorable) alongshore wind stress. The cross-shore profile of alongshore stress typically has an offshore maximum located some 200 to 300 km from the coast. The decay of the wind stress toward the coast defines a region of cyclonic wind-stress curl, where coastal upwelling is enhanced by curl-induced oceanic upwelling (Ekman pumping). During summer in the respective hemispheres, the region of cyclonic curl expands poleward in each boundary current...

The Seasonal Cycle of Wind Stress Curl in Subtropical Eastern Boundary Current Regions

http://digital.csic.es/bitstream/10261/49073/1/CanC_review_PiO2009.pdf

Sub-regional ecosystem variability in the Canary Current upwelling

Satellite Advanced Very High the continental slope of the Atlantic coast of Resolution Radiometer (AVHRR) imagery and Argos the Iberian Peninsula in a narrow (approximately tracked drifters have revealed the existence of a 100 km) vein, centered at a depth around 1000 m narrow, warm surface poleward current along the (Lacombe, 1971; Reid, 1979). Some recent Iberian coast during autumn and winter. Six observations (Ambar, 1984; 1985) indicate that near-surface drifter tracks indicated a net this poleward flow may extend from the bottom of northward flow between September 1986 and March the MIW (1600 m) to the top of the North Atlantic 1987, although individual drifter trajectories Central Water (NACW), i.e., the bottom of the also provided evidence of eddy activity and surface mixed layer at 100-200 m depth. Such episodes of equatorward flow. A SeaSoar survey poleward flows bound to the continental slope are during September 1986 in the region 37o-43oN, thought to be a common feature of sub-tropical 9o-11oW showed that poleward flow at that time eastern boundary regions (Wooster and Reid, was associated with the northward advance of a 1963). While there are numerous short term warm, salty tongue of water throughout the upper observations to show that similar flow can occur 400 m layer. Infra-red imagery confirmed the all along the eastern boundary of the northward penetration of the warm current and its sub-tropical gyre (Barton, 1989), few systematic progression around Cape Finisterre along the or long term observations are available to define north coast of Spain during the course of the the meridional extent and continuity of the winter. A similar situation is indicated by undercurrent. In other, similar areas, e.g., satellite imagery during other years. Current California (Huyer, 1983), it is found that during meter data show that poleward flow occurred along the upwelling season, when the trade winds the continental slope down to depths greater than dominate, the surface flow is equatorward over 600 m. Conductivity, temperature, and depth (CTD) the shelf, but may become poleward at times of casts show the presence of Mediterranean weak or northward wind. The seasonal variation Intermediate Water (MIW) at depths greater than of the surface flow off the Iberian coast is not 600 m. The MIW does not flow as a simple well established. northward flowing jet along the continental slope In September to October 1986, a cruise was off Iberia, but instead shows evidence of eddies undertaken off the Iberian coast to investigate within the flow. The poleward surface current is conditions over the continental margin. The in the opposite sense to the general summer resultant data set indicates that the season of circulation of the region, when cool upwelled upwelling had finished and that a regime of water is advected equatorward. It is postulated northward flow over the continental shelf and that the poleward flow is generated by slope was being established. In this paper, we thermohaline forcing when the southward trade describe characteristics of the circulation based winds, characteristic of the summer months, on shipboard, drifting buoy, and moored current weaken or reverse. Intermittent poleward flow meter observations. Satellite sea surface appears to be a common characteristic of the temperature imagery from a number of years Eastern Boundary throughout the North Atlantic (1982-1989) is used to show that the presence of from west Africa to the Norwegian Sea. a warm water mass extending along the Atlantic

/pdf/a-poleward-flow-along-the-atlantic-coast-of-the-iberian-2z0zcli28m.pdf

A poleward flow along the Atlantic coast of the Iberian peninsula

The development, persistence, and variability of upwelling filaments off the Atlantic coast of the Iberian Peninsula are examined by means of advanced very high resolution radiometer infrared imagery observed between 1982 and 1990. These observations indicate that the regime is broadly similar to that observed in the California Current system and is closely related to the large scale wind climatology of the subtropical gyre. Upwelling generally starts in late May or early June and persists until late September or early October. In May or June, a narrow band of cold water of quite uniform width is observed along much of the west coast of the Iberian Peninsula. This band has a “fringed” appearance; that is it consists of many narrow “fingers” of cool water extending 20–30 km offshore. The major filament structures generally do not begin to form until late July or August. The filaments appear first as bulges in the upwelling front. These bulges grow offshore to form filaments that reach their maximum length (200–250 km) in September. The lengths of the filaments gradually decrease until the filaments become relatively rare in late October.

Typically, five or six fully developed filaments are observed off the Iberian Peninsula late in the upwelling season. Most of these are associated with major topographic features of the region, in particular the large capes which are common to the north and south of the peninsula. It is therefore postulated that the dominant dynamical processes related to filament formation off Iberia is topographic forcing. The exceptions are two major filaments commonly observed along the more regular coastline of northern Portugal. It is hypothesized that these filaments are formed by flow instabilities resulting in meandering of the southward flowing jet. These instabilities may possibly be initiated by the large capes of northern Spain.

/pdf/development-persistence-and-variability-of-upwelling-h8xkh8slm2.pdf

Development, persistence, and variability of upwelling filaments off the Atlantic coast of the Iberian Peninsula

During the Galicia X cruise, from May to October 1989 an intensive collection of hydrographic data was carried out at a single station on the shelf off the western coast of Galicia. It allows us to follow the response of the water column to the intermittent equatorward wind stress during the upwelling season. Upwelling events occur with biweekly periodicity, bringing Eastern North Atlantic Water (ENAW) to the subsurface layer at our station. A trend of the thermohaline properties of the upwelled water to increase in time was observed. This seems to be mostly due to the southwestward displacement of the origin of this water mass during the year. Although the saltier and warmer ENAW is less nutrient-rich, nutrient levels increase because of the rapid remineralization of organic matter from the Rias, which takes place in the bottom water on the shelf.

/pdf/hydrographic-variability-off-the-rias-baixas-nw-spain-during-4mtygk5nmr.pdf

Hydrographic variability off the Rías Baixas (NW Spain) during the upwelling season

Observations and numerical simulations of the evolution of upswelling and the resultant coastal circulation in response to two wind events occurring along the Galician coast of Spain during the April 18-26, 1982 period are presented. In situ measurements include shipboard determinations of hydrographic and biological parameters, and wind stress estimates obtained from the ship winds and from surface pressure charts. Sea surface temperature information was derived from NOAA 7 satellite images, and pigment concentration information was acquired from the Nimbus 7 coastal zone color scanner. The indication from the simulations that the greatest upswelling will occur either at Cape Finisterre or along the northern coast was confirmed by observations, and it is suggested that wave disturbances propagate northward along the coast at a speed of 120-160 km/day, and that organic material formed north of Cape Finisterre is advected out to sea northwest of the cape.

/pdf/wind-driven-upwelling-in-the-vicinity-of-cape-finisterre-2lw6gae2wu.pdf

Frederico De Castillejo

Papers

Wind‐driven upwelling in the vicinity of Cape Finisterre, Spain