494 Tides of the Oceans 



than in the Atlantic Ocean, where they sporadically exceed 10 cm. The tidal 

 picture of the antarctic belt remains questionable until new observations are 

 available. Dietrich's presentation can only be considered as provisional. 



6. Tidal Currents in the Atlantic Ocean 



The Atlantic Ocean is at present the only ocean for which we have current 

 measurements obtained at a fair number of anchor stations; they permit the 

 formation of an approximate picture of the distribution of these currents in 

 the centre of this ocean, but of course, this can only be considered as an attempt. 

 Current measurements from an anchored ship present some difficulties, and 

 their results contain errors which are difficult to eliminate. In view of their 

 limited number, the few existing stations do not permit one to give a detailed 

 picture of the distribution of the currents. But in conjunction with the co-tidal 

 lines of the vertical tide we can get a good general idea. Most of these anchor 

 stations have been made by the "Meteor" Expedition and their results have 

 been published by Defant (1932) (see also Thorade, 1934, p. 1). Further- 

 more, there are three stations of the Pillsbury worked up in a modern way by 

 Schubert (1932, p. 378) and three stations of the "Michael Sars" and the 

 "Armauer Hansen" Expedition (Helland-Hansen, 1930; Ekman and 

 Helland-Hansen, 1931) and finally two stations of the second cruise of 

 the North Atlantic expedition of the "Meteor" in 1938 (published by Schu- 

 bert, 1944). In all, eighteen stations are available. Table 83 gives a com- 

 pilation of the main results of the analysis, for the semi-diurnal tide. The 

 measurements were made in various depths. In the table each quantity re- 

 presents an average value computed from the observations in different depths 

 which are often rather different from each other. This method eliminates, for 

 a large part, possible errors. The principal direction and phase of the current 

 for the individual stations have been entered in Fig. 204 and an attempt made 

 to draw co-tidal lines for tide currents. It is to be seen that the phases are 

 fairly uniform across the width of the entire ocean and supports the old pres- 

 entation of a tide wave progressing from south to north, whose tidal currents 

 have the form of a rotary current cum sole as required by Sverdrup's theory. 

 Figure 204 shows, of course, only approximately the distribution of the tidal 

 currents. It is quite possible that the uniform advance of the co-tidal lines 

 which were interpolated from the few available values, should be replaced by 

 co-tidal lines which are crowded over a short distance. The direction of the 

 tidal current off the American coast is southward, which is opposite to the 

 direction prevailing at the same time off the African coast which is in agree- 

 ment with a large amphidromy of the semi-diurnal tide in the North Atlantic. 



If we omit "Meteor" station 229, which is disturbed by the proximity of 

 the coast, 66 out of 77 current ellipses have a direction of rotation cum sole, 

 i.e., 86% of all cases agree with the direction required by the theory. The 

 ratio of the small to the large axis of the current ellipse should be theoretically 



