484 



Ocean Currents in a Non-homogeneous Ocean 



Fig. 219. Vertical structure in a convection current off a long straight shore (x-direction) 



for a homogeneous top layer of the vertical extent d and homogeneous deep water (D, 



frictional depth; unit of the velocity as in Fig. 218, according to Ekman). 



only below this, the current is directed towards the coast. If, on the other hand, 

 d> D, then there will be a normal gradient spiral in the top layer and a corresponding 

 inverse one in the deep water. If the water of the top layer is stratified, the general 

 current structure will be significantly changed (Fig. 220). Now the deep water will be 

 carried along, only to a lesser extent. The deeper the surface layer, the closer will the 

 flow parallel the coast and the lesser will be the eff'ect on the layer beneath. As in the 

 case of Fig. 218 the current is limited to the stratified top layer and its intensity falls 

 near the boundary layer almost to zero. 



2 



Fig. 223. The same as in Fig. 219 for a stratified top layer (according to Ekman). 



Ekman (1928 6) summarized these results and arranged them in a clear manner in 

 Fig. 221. Three alternative assumptions have been made on the thickness (in metres) 

 of the top layer d^\ 



(1) the top layer is divided into two homogeneous halves with a discontinuity 

 surface in the middle ( — x — x — ^); 



(2) the top layer is stratified so that in it a density current is generated with a velocity 

 distribution following a cosine-function ( — • — • — ) ; 



(3) in the top layer the velocity decreases linearly with depth and there is a dis- 

 continuity layer ( — o — ^o — ^). 



Velocity profiles for the currents produced are shown on the right-hand side of 

 Fig. 221 ; in the upper picture for a top layer the thickness of which is assumed equal 



