Latitude 10° 2 0° ^0° 40° 50° 60° 



a 6.2 3.9 2.7 2.1 1.7 1.5 

 r x 10 6 2.75 3.14 3.43 3.44 3. 30 3*30 



With the estimated angles 0, r is almost constant. This may 

 indicate that in the average for the whole layer of the gradient 

 current, frictional conditions are rather uniform in the different 

 branches of the circulation system, although under special con- 

 ditions significant local variations of the effective frictional 

 forces may occur. For the numerical integration of the differential 

 equation (11), however, an average value 



r s 3.3 x 10" 6 [sec" 1 ] 

 will he used. 

 IX. The wind stress at the sea surface 



Estimates of the total wind stress at the sea surface rest 

 largely on observations of the vertical distribution of mean wind 

 near the sea surface. Such wind profile measurements in the lowest 

 layers over the sea surface have been compared with the velocity 

 distribution in circular pipes, so that the interfacial stress could 

 be deduced from the measured wall stress in pipes. This method 

 simply applies the results of experimental, aerodynamical studies, 

 and is, therefore, based on the assumption that such a comparison 

 is justified. 



Regardless of the question as to how far the analogy between 

 the wall stress in pipes and the wind stress at the free sea surface 

 goes, there are still other objections against the method used , 

 especially with regard to the method of observing the average verti- 

 cal wind profile with cup anemometers at fixed "heights" above the 



36 



