Wind-Driven Currents

The upper ocean wind-driven current was described realistically for the first time by Walfried Ekman s landmark theory of 1905. The velocity distribution in the near surface layer of the ocean cannot be determined without additional information about the variation of the Reynolds stress vector with depth. Ekman (1905) assumed the Reynolds stress vector to be equal to the vertical shear of the mean current vector times a constant vertical eddy viscosity. The resulting current profile below the sea surface is the well known Ekman spiral with current speed decreasing exponentially with depth and current direction turning clockwise linear with depth from 45° right-handed to the wind stress vector at the sea surface. 

Although the details of the vertical structure of the wind-driven current in the surface mixed layer depend on the vertical distribution of the Reynolds stress in the surface layer, the vertical integrated wind-driven current, the Ekman transport, depends only on the wind stress at the sea surface. 

Brink, K. H., 1991. Coastal-trapped waves and wind-driven currents overthe continental shelf Annual Review of Fluid Mechanics, 23, 389-410. 

Waves cause significant water velocities over the bottom of Long Island Sound within a wave-affected zone that is confined to a shoreside area where the water depth is less than 18 m. Wind-driven currents occur only in the upper third of the water column throughout the deep water of the Sound. The tide is the dominant source of power for bottom pro-... 

As mentioned before, wind-driven currents are also one of the important currents for water quality and ecosystem in bays. 

There is clearly a need to better measure and document mass transfer coefficients (MTCs) or velocities in the 41 individual processes described in this handbook. It would be very useful to have available compilations of MTCs for specific chemicals in specific environmental settings thus providing guidance as to the likely range of values. It is understandably difficult to measure MTCs in the highly variable natural environment, even for example, in a relatively simple system such as the water-air interface of a small lake. Complications result from thermal and meteorlogical variability and the presence of particles. These variables can be better controlled in the laboratory in wind-wave tanks but this introduces problems of scale, wind-driven currents, and fetch. What is needed are careful experimental measurements in both... 

In Talon Charbonnel (1998, TC98), Charbonnel Talon (1999, CT99) and Palacios et al. (2003) we went one step further We included in the models the most complete description currently available for rotation-induced mixing, and we computed self-consistently the transport of the chemicals and that of AM due to wind-driven MC. We used the same input physics than that used with success by the Geneva group to explain several observational patterns of more massive stars (e.g. Maeder Meynet 2000 and Talon Charbonnel 2003 and references therein). 

Depth 0-200 m, photic, water-atmosphere interface, turbulent, wind-driven, variable temperature, above thermocline, no interactions with bottom Depth >200m, no light, high pressures, below thermocline, cold, no interactions with atmosphere or bottom, mostly lateral currents Depth >200 m, no light, sediment-water interface, no interactions with atmosphere, mostly lateral currents... 

FIGURE 2-2 Bickford Reservoir, a lake in central Massachusetts. Lakes such as this typically stratify during the summer season, but become fully mixed during the spring and fall. Water currents in a lake are mostly wind-driven and vary in velocity. On large lakes, wave action also becomes an important transport factor. (Photo by H. Hemond.)... 

Chemical d5mamics and mechanisms of reactions in the ocean-atmosphere system on time scales equal to and less than that of ocean circulation are evaluated by stud5nng the distribution of chemical compounds within the sea. In order to understand the processes controlling the chemical distributions and their rates, one must know something about how the ocean circulates. The following brief descriptive overview describes the main wind-driven and thermohaline current distributions. 

Price, J. E, Weller, R. A., Schudlich, R. R., 1987. Wind-driven ocean currents and Ekman transport. Science, 238, 1534—1538. 

Surface ocean currents respond primarily to the climatic wind field. The prevailing winds supply much of the energy that drives surface water movements. This becomes clear when charts of the surface winds and ocean surface currents are superimposed. The wind-driven circulation occurs principally in the upper few hundred meters and is therefore primarily a horizontal circulation, although... 

Wind-driven circulation occurs as a consequence of friction and turbulence imparted by wind blowing over the sea surface. This circulation pattern is primarily horizontal in movement and is responsible for transporting warm water from lower latitudes (warm) to higher latitudes (cold). Surface currents move water and carbon great distances within ocean... 

Dynamical interpretation to the SCS circulation pattern By assuming the SCS to be an enclosed basin, the basin-scale circulation pattern can be obtained from the Sverdrup stream function. And from the Sverdrup stream function in the interior region, the mass transport of the western boundary current (WBC) is 5 6 Sv and 3 4 Sv in winter and summer, respectively. They suggested that the upper layer basin-scale circulation can be mainly regarded as a wind-driven circulation forced by the wind stress vorticity, which indicates that the SCS circulation has strong regional characteristics. 

Major circular flow patterns in the oceans. The wind- driven eastward- and westward-flowing equatorial currents are blocked by the continents and rotate slowly in a clockwise direction in the North Atlantic and Pacific Oceans and in a... 

Deep-surface currents Pelagic Settling Deep, flow, essentially dear-water flows that are deep parts of surface wind-driven ocean currents Viscous fluid No slope or gentle slope As above As above As above Semicontinuous currents often with marked periodicities As above As above... 

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