Bottom water wind stress

Figur 33 1 Physical and biological upwelling response simulated by the Wroblewski (1977) 2-dimensional coastal upwelling model (A) The circulation in the transverse plane normal to the coast, the bottom topography, and the wind stress. The maximum u and w velocities in the field are —2.9 cm s and 1.4 x 10 cm s , respectively. (B) The daily gross primary production of the water column. (C) The distribution of phytoplankton. Contour intervals are 1 jimol N 1. Redrawn with permission from Wroblewski (1977).

Fig. 4. Departure of observed from predicted water level at NH, NL, and Np the mean flow recorded 2 m above the bottom at location D, and the relative wind stress as measured at NH during a winter storm, December 1972.

Fio. 4. Each line segment in the upper diagram shows the net flow of water over a 12.4-hr tidal period. The current meters were at elevations of 0.88rf (A), 0.46water depth. The lower diagrams show resultant current vectors obtained from meter A (the one nearest the surface) and, for comparison, the resultant surface wind for the same time intervals. The surface water follows the wind stress closely the flow near the bottom is unrelated to the wind stress. The meters were set 7.4 km north of Eatons Neck. 

We have previously reported that, although most storms do not alter the bottom-water resultant flow vectors, the probability of large water speeds over the bottom is increased (Bokuniewicz et ai, 1975b) when the wind stress is high. We now present further evidence on this effect. A periodogram calculated for a current meter record obtained in the western end of Long Island Sound is presented in Fig. 6. Three tidal peaks are... 

In addition to raising waves on the water surface, winds will set the surface layers of water in motion in the direction of the wind stress or, if the water is sufficiently shallow, set up a circulation pattern extending to the bottom. Pickard and Rodgers (1959) have shown, for example, how an up-estuary wind can set the surface layer of water in the Knight Inlet (B.C.) in motion against the estuarine circulation. Elliott (1978) has demonstrated the importance of wind stress in determining the circulation in the Potomac estuary. To have much influence on estuarine sedimentary processes, however, the wind-driven circulation must penetrate to the bottom, which is likely to happen only in relatively shallow estuaries. In... 

A storm is a violent disturbance of the atmosphere attended by wind and usually by rain, snow, hah, sleet or thunder and hghtning. A storm surge is the accumulation of water at shallow depths due to wind stress and bottom friction together with the atmospheric pressure reduction that occurs in conjunction with severe storms. The probable maximum storm surge is the hypothetical storm surge generated by either the probable maximum tropical cyclone or the probable maximum extra-tropical storm. 

In the above, is the surge component due to the wind stress, is the wave setup, p is the mass density of water, g is the gravitational constant, h is the local water depth, Tsx and are the surface and bottom shear stresses, respectively, and similarly for the -direction. The coordinate direction, x is oriented shoreward and a right-handed coordinate system is considered. 

Fig. 32.6. Results of measurement of (a) water level, (b) wind, (c) instantaneous currents at surface, (d) bottom layers, (e) residual currents at surface, and (f) bottom layers, respectively, illustrating the dependency of instantaneous currents on tide and residual currents on wind stress at Stn. 1 in 2005.

Although a flow in the down-wind direction is easy to understand, density structure and rotation of the earth make it more complicated. To simplify our discussion, let us consider the rectangle bay which is very small and has a uniform depth. It is assumed that Coriohs force and stratification effect can be neglected. When the wind blows over this bay, it generates a shear stress at the sea surface. The surface water moves in response to the wind-shear stress the water surface of the leeward side becomes higher and the windward side becomes lower (see Fig. 32.7). If the water pressiues at the seabed are compared at this time, the water pressure of the leeward will become high because of the effect of wind stress. As a result, a flow which returns to the upwind direction occurs at the seabed. Consequently, a vertical circulation, for which the direction of the flow are opposite at the surface and bottom, occurs. In this mechanism, the water near the seabed as well as the surface responds to a wind in comparatively short time, and moves to the upwind direction. 

Wind movements in the atmospheric BL directly impact water turbulence and currents in the surface layers. However, the role of wind in generating turbulence and currents in the bottom-water (i.e., hypolimnion) above the sediment bed is the issue of interest here. Wind stress on the surface moves water masses in bulk generating internal water movements that are transmitted deep into the water column resulting in bottom currents. However, these are also sporadic in direction, magnitude, and duration. 

As the plant matures, more nodes and lateral stems will be produced. The stems have a variety of functions. The stem creates and holds the leaves at proper intervals while it transports water and food to the rest of the plant from bottom to top. When the stem is stressed by the blowing wind, it creates cellulose which makes the stem stronger to resist being blown over. 

Wave-induced acceleration of bottom mud, total pressure, and pore pressure were measured at a deep site in the lake (Fig. 27.1(a)) 0.2 m below the mud-water interface.The vertical amplitude of acceleration is plotted against the wind speed in Fig. 27.13. There is an evident trend of increasing amplitude with wind speed. Acceleration is a manifestation of heave, and as seen, 3.2 ms may be taken as the threshold speed for the onset of heave. The effective normal stress [Pg.799]

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