Variation of the drag coefficient with wind and wave state
Byars, Beverly J.
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The dissipation method is used to obtain estimates for the friction velocity, U>t, as well as values for the neutral drag coefficient, C-^jj, for data collected from a coastal tower off San Diego, California. C-q-^ is found to be independent of the ten-meter height windspeed, U-j^q, for velocities between 4-9 m/sec. Its value is estimated to be (0.94+0.4)10 which compares well with values by Smith (1980) and Large and Pond (1981). Definite trends in C-q-^ with fetch and sea state are also observed. Drag coeffcient estimates are found to be higher for short fetch than for long fetch conditions. C-q^ is also seen to increase sharply just before frontal passages and during sea breeze conditions when the waves are actively growing. With the windspeed and wave field reaching equilibrium, C-q-^ is found to decrease with time to a smaller and more constant value.