Wind Stress on a Coastal Water Surface

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by S. A. Hsu,

Document Type: Proceeding Paper

Part of: Coastal Engineering:

Abstract: Simultaneous measurements of horizontal wind velocity above the water surface, air and water temperature difference, and water level were made during the summer of 1971 at an exposed field site off the northwest coast of Florida. Three identical vertical arrays of six-cup anemometers were used; they were located in the surf zone, in the area between the inner and the outer bars, and on the outer slope of the outer bar. The distances of these three stations from the mean shoreline were approximately 30, 130, and 230 m. Mean water depths were 1.5, 4.3, and 5.0 m.Analysis of the profile data under adiabatic and onshore wind conditions indicates that better than 90 percent of the valid wind profile measurements are logarithmic. It was found from the nearly fifteen hundred 15-minute logarithmic wind profiles that the shear velocity U* was not a linear function of wind speed, as is usually assumed in coastal applications, but had a functional relationship with velocity at 10 m or U10m (from 0.5 to 8.5 m/sec), such that U* = 0.37 U10m2/3.Comparison with similar investigations in deeper water and oceanic regions was also made.

Subject Headings: Water surface | Sea water | Wind engineering | Estuaries | Environmental issues |

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