Effect of Wind on the Mass Field and on the Density Current 



545 



will decrease with depth-changing sign at the layer of no motion. This will modify the 

 mass field which then can no longer remain barotropic. The isosteric surfaces must slope 

 transversally ; the mass field becomes baroclinic. The structure of the associated density 

 current can be computed by means of ordinary methods from this mass field. The 

 primary factor will now no longer be the water stratification but rather the current, 

 while the water stratification can be regarded as a consequence of this current. 



Palmen investigated data for the Gulf of Finland for steady westerly and steady 

 easterly winds and distinguished between a west type and an east type. He deduced 

 mean mass fields over a cross-section for these two cases from the large amount of 

 data available. In the east type the lighter surface water lies in a wedge-form at the 

 Finnish coast with the isosteres sloping downwards from south to north, while in 

 case of the west type conditions are reversed. Figure 252 shows the distribution of density 

 for the two opposite types. The interpretation is simple: the west wind produces a 

 drift current in which the transport is directed towards the Estonian coast where the 

 lighter surface water will pile up. For an east wind the opposite occurs. Palmen has 

 demonstrated the reality of these changes in sea level between the northern and southern 

 sides out of observations of water level in Hango, Reval and Helsinki. For the east 



Estonio 



Finland 



J 100 



Fig. 252. Normal density distribution in the cross-section Aransgrund-Kokskar (Fennic 

 Bay, 25"' E.); at, values. , east type; , west type (according to Palmen). 



2N 



