SECT. 2] 



SMALL-SCALE INTERACTIONS 



B. Eddy -Correlation Results 



59 



Some measurements of the shearing stress by the eddy-correlation technique 

 have been made by Mcllroy and also by Deacon over Port Phillip Bay (Deacon, 

 1957) and by Vinogradova (1959) over the Caspian Sea. The equipment used 

 by Mcllroy (1955) was rigged at a height of 6 m above the surface using a boom 

 from a jetty 150 m long, while Deacon's measurements were made at a height 

 of 12 m on the foremast of a small vessel. Vinogradova's apparatus was mounted 

 2 m above water level 50 m off- shore where the water depth was 5.5 m. Condi- 

 tions of neutral stability were not experienced in these trials but a neutral 

 value of the drag coefficient for winds of around 7 m/sec can be estimated 

 from the results tabulated below. The stability conditions are indicated by 

 ATjui"^, where AT°C is the difference in temperature between the air-sea 

 surfaces, and W2 the 2 m wind speed in m/sec. 



From the determinations in Table II, a neutral value of approximately C2 = 0.0024 

 would be expected and for the 10 m reference level cio = 0,0017 for uio ~ 9 m/sec. 



At lower wind speeds, Vinogradova's observations on two days, one of stable 

 conditions (7 runs) and the other unstable (15 runs), indicate a neutral value 

 of C2~ 0.0025 corresponding to cio~ 0.0017 for a mean wind speed of 4.2 m/sec. 



The drag coefficients from the eddy-correlation technique are in general 

 agreement with those derived from the wind-profile studies although as yet 

 results are too few for any close comparisons to be made. 



Also in satisfactory agreement with these results is that of Charnock, Francis 

 and Sheppard (1956) derived from a study of the wind structure of the trades. 



For large fetches of the wind over open sea, Brocks (North Sea) finds from 200 near- 

 neutral profiles (air-sea temperature difference — 0.3°C to -|-0.2°C): 



cio = 1.1 X 10-3, 



again with no significant variation over the range 1-10 m/sec. 



A few observations over open sea to the southward of Port Phillip indicate for neutral 

 conditions cio~l-2xlO~3 (Deacon 1961). In this case the wind-speed range was 3 to 

 13 m/sec. 



