Oceanic Circulation and Temperature 

 the motion will be as follows: Imagine a spiral 

 stairway so situated that the edge of the top step 

 is directed at an angle of 45" to the right of the 

 wind velocity, thus coinciding with the arrow (Vo) 

 of figure 16. Now if, as we descend, the steps are 

 shortened so as to have in succession the lengths 

 of the arrows in the diagram, the length of each 

 will represent, in magnitude and direction, the 

 velocity of the water at that depth. And at a depth 

 corresponding to a half turn the velocity of the 

 water is only 4 per cent of its initial value, and 

 decreases rapidly from there downward. So, for 

 practical purposes, we may neglect the motion be- 

 low that depth. This depth increases with the 

 wind velocity, but decreases with the latitude. At 

 latitude 35", if the wind velocity were ten miles 

 per hour, the depth would be about twenty-five 

 fathoms. 



>• ■ 



U 



3 



z Y 



s / ^ 



Bottom or Occan 



Figure 16 Figure 17 



The direction and velocity Upwelling of ocean water, 

 of the water at increas- 

 ing depths. 

 Suppose the wind has a component parallel to 

 the coast line, and the water lies to the right when 

 looking in the direction of that component (in the 

 northern hemisphere). Suppose, further, that the 

 depth of the water exceeds about twice that of 

 the "wind current"*. Then, according to Ek- 

 man's theory, surface water will be carried to the 

 right of and along the coast, thus causing a de- 

 pression of the water level. The corresponding 

 reduction in pressure on the bottom will cause a 

 flow of the deepest water toward the coast and up- 

 • Wind-current is a technical term used to denote the 

 current in the upper part of the water produced by wind 

 over the open ocean. 



137 



