772 



[CHAP. 2.3 



normally these are not very valuable. The data from coastal areas are not all 

 of the same degree of accuracy. Sometimes the duration of observation is too 

 short, in other cases they are disturbed by local effects and, therefore, they are 

 not representative for the open sea (Table I contains several harmonic constants 

 from the Atlantic Ocean). The same is true for observations of tidal currents 

 where there is only a very small number of observations from the open sea, 

 chiefly performed by research vessels. In adjacent and marginal seas the situa- 

 tion is somewhat more favourable ; in the North Sea in particular there are a 

 considerable number of observations of tidal currents. The following figures 

 demonstrate the behaviour of tidal currents from surface to sea bottom in the 

 neighbourhood of Heligoland and in the English Channel. Fig. 3 contains 

 velocity and direction of tidal currents at three stations in the German Bight 

 approaching the Elbe estuary. In Fig. 4 the elhpses of tidal currents from 

 anchor station Meteor No. 36 ((p = 28° 8'S, A= 19° 21'W) in the South Atlantic 

 are drawn up. These figures show, consequent upon the influence of friction 

 and Coriolis force, a variation of tidal ellipses with depth. Table II contains 

 information about tidal currents in the deep Atlantic Ocean. 



Table II 

 Observed Currents in the Deep Sea 



