552 



Internal Waves 



tide-generating forces in essentially the same way, with the exception of small 

 deviations in the upper layers. The direction of the major axis of the semi- 

 diurnal current ellipse was N. 40° E. the maximum velocity 8-3 cm/sec and 

 the phase 0-5 lunar hours (Gr.). The ratio of the minor to the major axis 

 was 043, its direction was cum sole. But besides this uniform tide wave 

 there appeared also a 17-hourly wave, which was very much in evidence in the 

 curves of the tidal current through beats. The analysis of the curves gave the 

 values shown in Table 97. These fluctuations leave no doubt that it represents 



Table 97. Anchor Station "Altair" ( 16-20 June 1938, 44°33'7V., 38°58'^J. 

 Analysis of the current observations for a 17 h Wave 



* Refers to Oh G. M. T. of 17 June 1938. 



an inertia oscillation: according to theory its period 12/sin</> = 171 h, the am- 

 plitudes of both components are equal, the current is turning to the right 

 and the east component follows the north component by I period. Strikingly, 

 there exists a differentiation with depth. The upper layer from the surface 

 to 15 m had a completely inverted course compared with the layer from 30 

 to 100 m. There seems to exist again a displacement of half a period (8-5 h) 

 between the middle layer and the depth of 800 m. Since the upper layer down 

 to a depth of 100 m shows a well-developed discontinuity in the density 

 (maximal values at a depth of 25 m), it may be assumed, that the 17-hourly 

 wave has the character of internal waves. This was also demonstrated by 

 working up the repeated serial observations over 90 h. Temperature and 

 salinity values in this layer showed a uniform vertical displacement of the 

 water-masses with a phase of 10 5 h and a mean amplitude of 3 m. Similar 

 conditions prevailed in a depth between 350 and 450 m, where a discontinuity 

 layer was less pronounced. 



From the structure of the entire ocean region near the "Altair" peak it 

 can be concluded, that the length of the oscillating system was about 1 50 km. 

 Furthermore, ^' = 25 m, h = approximately 1500 m, q' = 10263 and 

 q = 10278; thus q—q' = 15xl0~ 3 . According to equation (XVI. 39) the 

 period of the free oscillation of the entire system will be 16-98 h. Compared 

 with the inertia period of 171 h, the difference is very slight. The equilibrium 

 of the entire ocean region near the "Altair" peak was probably upset by 



