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Prologue
Published in Vikram M. Mehta, Natural Decadal Climate Variability, 2020
The 850 hPa winds are generally representative of winds down to the ocean surface and, therefore, the 850 hPa winds can be approximated as ocean surface winds. Winds at the ocean surface exert a force, known as wind stress, on the surface water. This wind stress drives currents which constitute the so-called wind-driven ocean circulation. Figure 1.5 shows major, annual-average currents in the world oceans. A comparison of Figure 1.5 with Figure 1.1 shows that the streamlines of currents, shown by black lines and arrows, in the former figure are generally similar to wind vectors in the latter figure. Figure 1.5 also shows temperatures of major currents (red and blue arrows). Poleward flowing currents are generally warm and equatorward flowing currents are generally cold. The clockwise and counter-clockwise flowing currents, known as gyres, play very important roles in DCV phenomena because their interactions with the atmosphere can generate anomalously warm/cold water which is then transported by the gyres at their slow speeds over ocean basin scales; and because of their interactions with slow-moving, ocean basin scale waves.
Dispersion in Shallow Estuaries
Published in Björn Kjerfve, Hydrodynamics of Estuaries, 1988
Wind-driven currents are forced by the wind stress acting on the water surface.1 Nontidal forcing is the result of sea-level variations at the open boundary of the estuary having frequencies lower than the tides. These variations in turn are caused by meteorological forcing.8-12 Rectification of tidal currents associated with nonlinear interaction of tidal waves is described in van de Kreeke,13,14 and van de Kreeke and Chiu.15 Information on rectification of tidal currents due to changes in topography can be found in Zimmerman.16 Freshwater inflow results in a net or residual velocity. For example, in the classical estuary the residual velocity equals uf = Qr/A, referred to as the freshwater velocity, where Qr is the river discharge and A is the cross-sectional area of the estuary.
Modelling of estuaries
Published in P. Novak, V. Guinot, A. Jeffrey, D.E. Reeve, Hydraulic Modelling – an Introduction, 2010
P. Novak, V. Guinot, A. Jeffrey, D.E. Reeve
Wind stress is a significant driver of coastal ocean circulations. One well- known result of this is known as ‘wind set-up’. This is essentially a balance between the wind stress and the pressure gradient force. At the coast, wind set-up is a well-known phenomenon for which there are empirical prediction formulae. In fact, on the open coast wind set-up is a minor contributor, as a process known as ‘wave set-up’ is usually dominant (see Chapter 12). It is a similar process in that waves create a ‘radiation stress’ that is balanced by a gradient in surface elevation. Here we use a simplified form of the equations to illustrate the physics of wind set-up.
Ocean surface currents estimated from satellite remote sensing data based on a global hexagonal grid
Published in International Journal of Digital Earth, 2023
Wenbo Wang, Huijun Zhou, Senyuan Zheng, Guonian Lü, Liangchen Zhou
The ocean surface wind stress is the main driving force for generating Ekman currents. Thus, the ocean surface wind stress should be calculated to obtain the velocity of Ekman currents. Wind stress is a force on the ocean’s surface caused by the viscous effect of the molecules between the two layers of fluid when the wind-driven airflow moves relative to the ocean currents. The block calculation equation of the wind stress vector is: where (τx, τy) is the wind stress field, ρa= 1.2 kg/ is the air density, V10 is the wind speed value at 10 m above the ocean surface, (u10, v10) is the wind speed value, and is swaying coefficient. The scheme of is as follows:
Ocean mesoscale structure–induced air–sea interaction in a high-resolution coupled model
Published in Atmospheric and Oceanic Science Letters, 2019
Pengfei LIN, Hailong LIU, Jing MA, Yiwen LI
To evaluate the high-resolution simulation, SST values from the Advanced Very High Resolution Radiometer and Advanced Microwave Scanning Radiometer (Reynolds et al. 2007) for 2003–08 and sea level anomaly (Ducet, Traon, and Reverdin 2000) values from Archiving, Validation, and Interpretation of Satellite Oceanographic were used. Wind stress and wind speed values at 10 m were obtained from Quick Scatterometer (QuickSCAT Liu et al. 2000). Latent and sensible heat flux (LHF and SHF respectively) data from the Japanese Ocean Flux based on Use of Remote Sensing Observations, version 2 (Kubota and Tomita 2007), were also used.