Models for estimating offshore winds from onshore meteorological measurements |
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| Authors: | S A Hsu |
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| Institution: | (1) Coastal Studies Institute, Louisiana State University, 70803 Baton Rouge, Louisiana, USA |
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| Abstract: | To understand and estimate wind speed differences across the coastal zone, two models, one theoretical and another semi-empirical, have been developed and verified by available data sets. Assuming that: (1) mean horizontal motion exists across the coastal zone; and (2) the geostrophic wind does not change appreciably at the top of the planetary boundary layer (PBL), the equation of motion in the direction of the wind can be reduced so that 341-01, where U, H, and C
D are wind speed, height of PBL, and drag coefficient over the sea and land, respectively. For practice, C
D SEA has been modified from a formula with U
LAND as the only input. H
SEA may be estimated routinely from known H
D LAND
LAND and the temperature difference between land and sea, which can be provided by such means as remote sensing from meteorological satellites. For a given coast, Cmay be estimated also. This formula is recommended for weather forecasters. The semiempirical formula is based mainly on the power law wind distribution with height in the PBL. The formula states that 341-02. Simultaneous offshore and onshore wind measurements made at stations ranging from Somalia, near the equator, to the Gulf of Alaska indicated that values of a and b are 2.98 and 0.34 with a correlation coefficient of -0.95. For oceanographic applications, a simplified equation, i.e., 341-03, is also proposed. |
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