General Theory of Ocean Currents in a Homegeneous Sea 



435 



or greater there is no essential difference as compared with the frictionless case 

 (hr = 0, G = oo). For reasonable values of H and / Gortler estimated the magnitude 

 of G as between 3 and 80, depending on the intensity of U, the latitude and the rough- 

 ness of the bottom. This shows that for actual conditions in nature everything is the 

 same as in the case of no frictional influence. This is important for the practical use of 

 the above results. The effect of the topography of the sea bottom on the course of 

 the ocean currents has been clearly demonstrated for many oceanic regions. Ekman 



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Fig. 187. Upper picture: stream line pattern for a crossing of a bottom ridge depending on 

 friction. Lower picture: vertical cross-section through the bottom ridge. 



by using these principles was the first to offer an explanation for the striking 

 bending of the current trajectories, of the dynamic isobaths south of the Newfound- 

 land Banks (Helland-Hansen, 1912) which was not understood by simple reasoning. 

 The course of the stream lines is in good qualitative agreement with that given by 

 theory for the changes in depth actually present even if a closer qualitative examina- 

 tion of the phenomenon was not possible. 



The dynamic evaluation of the observational data made by the "Meteor" expedition 

 in the South Atlantic has afforded a good example of these effects of the bottom topo- 

 graphy (Defant, 1941 b). This example makes it very probable that the large irregulari- 

 ties in the east-west course of the dynamic isobaths that were found in the western 

 part of the convergence zone between about 25° and 50° S. have a fixed position and 

 can be attributed primarily to the morphology of the sea bottom. If the lines of con- 

 vergence and divergence for this disturbance are traced on transparent paper and laid 

 over a depth chart the relationship between the two phenomena shows unmistakably. 

 These conditions are illustrated by a diagram in Fig. 188. The lower part of the figure 

 shows two depth profiles at 30° and at 35° S. extending from the South American 

 continent to 0° W. ; they indicate the course of the bottom irregularities running in a 

 meridional direction as far as the mid-Atlantic Ridge in this part of the South Atlantic. 

 In the upper part are shown the stream lines plotted according to the dynamic isobaths 

 over the area from 30° to 45° S. Every "wave trough" in the bottom corresponds to a 

 bend contra soletn in the stream lines (here the reverse of the conditions as shown in 



