368 



The Representation of Oceanic Movements and Kinematics 



currents of the surface layers is untenable, and that the deeper water layers are also 

 involved in the surface current systems. An example of this type of representation is 

 given in Fig. 156 which shows the surface currents to the south of Africa during May 

 according to Merz (1925). A line of convergence runs right across it separating the 

 steady broad west wind drift in the south from the Agulhas Current south of Africa. 

 Charts of this type do not indicate the velocity of the current, its prevalence or the 

 amount of data on which it is based; velocity is mostly indicated by thin dotted lines 

 (nautical miles per day). Because of gaps in the available data current charts such as 

 these, constructed according to strictly hydrodynamic principles, are naturally not 

 certain in all details, but the individual stream lines and singularities support each 

 other by means of their course and position and thus offer the clearest possible picture 

 of the water movement. 



Another representation of essentially the same type was chosen by Helland- 

 Hansen and Nansen (1909, p. 9) in which the stream lines are represented by a 

 series of short arrows of more or less equal length (Fig. 157). Also here the velocity 



LT — in 



■^k^} 



J^-x 





Fig. 157. Mean currents at the sea surface of the European North Sea (according to Helland- 



Hansen and Nansen). 



