184 



MALKUS 



[chap. 4 



ATLANTIC 

 MEAN WIND STRESS 



Fig. 42. Mean wind stress for January over the North Atlantic computed from transfer formula 

 (17). (After Scripps Institution of Oceanography, Oceanographic Report No. 21, 1950.) 



The computations for the Pacific and Atlantic Oceans were carried out some- 

 what differently. In the Pacific, the basic data were the wind roses of the U.S. 

 Hydrographic Office Pilot Charts for each month. Air densities were calculated 

 from the mean pressure and temperature distributions. The U.S. Weather 

 Bureau Atlas of Climatic Charts of the Oceans was used to assess the wind-speed 

 distribution about the mean for each Beaufort number. In tropical regions 

 (5°S to 30°N latitude), a Gaussian distribution was believed satisfactory, with 

 a standard deviation of one-half the Beaufort interval. In temperate regions, 

 the speed distribution proved highly skewed with an average u composed of 

 many winds slightly less than u and a very few much greater. Histograms were 

 therefore constructed for each Beaufort interval from the climatic charts and 

 the mean stress for that interval computed numerically from the histogram. 

 The resultant stress in each quadrangle was finally obtained from the frequency- 

 weighted sum of rectangular components. Fig. 38 shows the mean annual stress 

 distribution for the Pacific, while Figs. 39 and 40 are reproductions of their 

 results for the single months of January and July respectively. Charts for each 

 month and season also appear in the Scripps Report, showing vector resultant 

 stress and corresponding charts for its north- south and east-west components 

 suitable for stress curl computations. 



For the Atlantic, the basic data were the Summary of Marine Data cards of 

 the U.S. Weather Bureau and the Monthly Meteorological Charts of the 

 British Air Ministry, which also give mean Beaufort interval and per cent 



