552 



Effect of Wind on the Mass Field and on the Density Current 



These equations have been tested by the "Carnegie" and "Bushnell" observations 

 of corresponding areas (approximately between 160° to 80° W. and 10° S. to 20° N.) 

 and showed good agreement with the values derived from the observations. The 

 theoretical values were calculated from the distribution of wind stress obtained from 

 the wind field given in oceanic climatological charts; thereby use has been made of 

 formulae (XIII.48 and 49). Figure 254 shows the excellent agreement between the ob- 

 served and theoretical meridional distributions oi APjAx and M^. It should be kept in 



25M 



Fig. 254. Picture to the left: theoretical and observed values APjAx in two sections of 

 "Carnegie" and "Bushell" stations. Picture to the right: Latitude dependence of the longi- 

 tudinal mass transport computed by two independent methods. (M^ = eastward mass 

 transport in tons per sec through a column of 1000 m depth and 1 m width). 



mind that the theoretical values are derived from mean wind conditions while the ob- 

 served values are based on some oceanographic stations made at different times of the 

 year. From these results it can be concluded that mass structure and mass transport 

 of the currents in the eastern equatorial areas of the Pacific can be regarded as a con 

 sequence of the average shearing stress of the air currents on the surface of the sea. 

 This conclusion should also be valid for the equatorial currents in other oceans. 



4. Velocity Computations of Oceanic Surface Currents in the Equatorial Regions 

 from Wind Data 



The currents in the equatorial regions can, as a first approximation, also be regarded 

 as the result of a drift current and a gradient current of the type described by Ekman. 

 However, at the equator itself the two components are indeterminate and the geo- 

 strophic approximation gives infinitely large values. In dynamic calculation these areas 

 must therefore be excluded. The question of how to calculate the currents in the 

 immediate vicinity of the equator from oceanographic data has been dealt with by 

 Weenink and Groen (1952), which gave an exact solution to the problem and by 



