General Theory of Ocean Currents in a Homogeneous Sea 



415 



offerees for each layer of the "elementar" current can be constructed. Figure 178 shows 

 these force diagrams for always one level of the three current layers. In the surface 

 current the frictional vector is directed to the side of the gradient vector pointing in the 

 direction of the water movement, and rotates in a clockwise direction with decreasing 

 intensity when going downwards and vanishes at the frictional depth. In the deep 



B. 



(b) 



iC 



(c) 



Fig. 178. Schematic diagram offerees for three levels of the "elementar" current (Northern 

 Hemisphere): {a) surface current, (Jb) deep current, (c) bottom current. OG, OC and 

 OF vectors of pressure gradient, of Coriolis force and of frictional force; v = velocity 

 vector in the level under consideration; V = velocity vector of the deep current; 

 w = vector of the velocity difference: v — V. 



current, gradient and Coriolis force balance each other without any frictional effect. 

 In the bottom current the frictional vector is directed to the side of the Coriolis force 

 pointing more or less in the opposite direction to that of the velocity and rotates 

 anticlockwise while approaching the bottom. From this distribution it can be realized 

 that in the surface current the frictional vector corresponds to a driving shear stress 

 which takes its strength at the sea surface from the energy of the wind, while in the 

 bottom current it indicates the retarding effect of the underlaying bottom topography 

 (break on the motion). 



(e) Drift and Gradient Currents according to Observations; Piling up of Water by 

 Wind {''Windstau'') 

 The two parts of the "elementar" current are never developed in the ocean in pure 

 form and it is to be expected that pure drift currents in the ocean will always be some- 

 what masked by the effects of superimposed gradient currents. It will therefore not be 



