408 



General Theory of Ocean Currents in a Homogeneous Sea 



the sea surface it cannot contribute to the equalization of the sea surface slope. This 

 can only be accomplished by the bottom current which always has a component in the 

 direction of the pressure gradient, i.e. a transport of water from a higher to a lower 

 level. This component does the work required to overcome bottom friction. 



Fig. 173. Vertical structure in a pure gradient current (according to Ekman). 



The transports (current amounts) M^ and My of a gradient current can be calculated 

 by integration between and d of equation (XIII. 32), after its multiplication by p. 

 In case of no bottom current the current component M^ would be Upd and it becomes 

 smaller due to the velocity decrease at the bottom. One obtains 



M^ = Upd - U 



Dp 



M. 



Dp 



Itt 



For depths less than D the effect of bottom friction is noticeable throughout the entire 

 water layer, and the more so the smaller the ratio djD. The curves in Fig. 174 illustrate 

 the gradient current at depths 1-25 D, 0-5 D and 0-25 D. The angle of deflection 



d=i-zsD 



Fig. 174. Vertical structure of gradient currents for ocean depths d nearly equal or smaller 

 than the lower frictional depth D (for more detail see Fig. 172). 



