452 



Tides in the Mediterranean and Adjacent Seas 



ice does not participate in the tidal motion and down to a depth of 35 m the velocity of the current 

 is too weak to be measured. Below this depth there is a rapid increase of the velocity of the 

 current; the maximum occurs in the discontinuity layer of the density at 42 m (see the vertical 

 distribution of the density a t ); then the velocity decreases towards the bottom. The current figures 

 to the right under B show a rotation cum sole in all depths, but towards the bottom the ellipse be- 

 comes narrower and is turned to the right in comparison with the upper layers and maximum 

 current occurs earlier. 



The lower presentation of Fig. 191 refers to a theoretical computation of these currents, 

 assuming that the upper and bottom layer had a constant eddy viscosity separated by a layer of 

 no-eddy viscosity, which coincided with the discontinuity layer, which has great stability. The 

 computed currents deviate, of course, from the observed ones, because the discontinuity layer is 

 replaced in nature by a gradual density increase. But there is agreement as to the main features, 

 so that there is no doubt that the rotation of the earth and the turbulence varying in the vertical 

 direction determine the character of the currents at the observed station. 



22. The Tides in Inland Seas 



In order to determine the order of magnitude of the tides in inland seas 

 of various dimensions, let us refer to the equations in Chapter IX, para. 3, (b); 

 (p. 293). Table 71 shows that in small, shallow seas the tidal ranges can be 

 expected at spring tides to be of the order of magnitude of 2-3 mm, which can 

 increase to 10 cm and more for large seas with a long period of free oscillation. 



Table 71. Range of the tides in lakes 



High water 



| western end 

 I eastern end 



3h| 

 9h 



centre meridian time 



The amplitude and the phase of such forced tidal oscillations in inland seas 

 have only some value if it is possible to subject a long series of observations 

 collected by very sensitive limnographs to a harmonic analysis; otherwise the 

 result will be inaccurate, because the influences caused by the free oscillations 

 (seiches) and other unperiodical variations like those caused by wind and air 

 pressure will be large compared to the small tidal amplitude. The problem is 

 the same as the analysis of the atmospheric tides from ordinary barometric 

 registrations, which was solved successfully, even for stations at higher lati- 

 tudes, where the unperiodical disturbances in atmospheric pressure are larger 

 than the very small atmospheric tides (see Bartels, 1928, p. 163). 



