602 



The Tropospheric Circulation 



the mean density distribution they took Reid's model (1948) which is generally 

 applicable in equatorial regions. The wind drift and gradient current were super- 

 imposed correspondingly considering the boundary conditions, and finally the vertical 

 velocity in the upper mixed layer was calculated using the continuity equation. 



Figure 277 shows the dependence on the latitude of the horizontal velocity components 

 u and V at the sea surface and the horizontal wind stress Tx, acting only in zonal 

 direction. It is evident that a strong equatorial counter current is formed between 



— •(Equatorial Counter Currency 



-35 -30 -25 -20 -15 





20 25 30 



0€ 04 0'2 OO 

 DYNE/Cm2 



Fig. 277. Latitude dependence of the horizontal velocity components u and v at the sea 

 surface and the horizontal wind stress T^ acting only in zonal direction on the ocean surface. 



2-5° and 1 1° N. in the area of weak westward wind stress between the strong north- 

 east and north-west trade winds. All the velocity components decrease somewhat 

 with depth down to the lowermost boundary of the upper mixed layer, the w-com- 

 ponent of the equatorial counter current decreases least so that almost uniform values 

 are found throughout the entire top layer. The vertical velocity resulting from the 

 continuity equation is shown in Fig. 278. Its distribution is rather noteworthy. It 

 shows : 



(1) very strong upwelling at or near the equator, this is the equatorial divergence; 



(2) strong sinking at the southern boundary of the counter current; and 



(3) fairly strong upwelling at the northern boundary of the counter current. 



The vertical velocity is of the order of lO-* and 10"^ cm sec"^. Farther to the north 

 the velocities are small and irregularly distributed. Considering that the Reid model 

 is only a crude approximation of true conditions and especially that the wind-stress 

 distribution with zonal components only can hardly correspond to actual conditions, 



