376 



Tides in the Mediterranean and Adjacent Seas 



part where they reach 3-4 cm. The diurnal tide (Fig. 157) has a large 

 amphidromy contra solem in the central basin; it includes the two gulfs in 

 the north and the north-east. The amplitudes of this wave are of the same 

 order of magnitude, mostly even greater than in the Kattegat and in the 

 Danish waters. This points to the fact that the diurnal tides are generated 

 in the Baltic itself, whereas it can be assumed that the semi-diurnal tides are 



Fig. 157. Co-tidal lines of the K t tide (0°, 90°, 180° and 270° correspond to Oh, 6 h, 12 h 

 and 18 h sidereal time; amplitude in cm) (Witting). 



influenced through the Belts and the Sund. According to the considerations 

 on page 194, the period 7} of the principal free oscillating system Kieler 

 Bucht-Mecklenburger Bucht, Darsersill, Baltic, Gulf of Finland, is 276 h. 

 From this follows that for the semi-diurnal tides v = T f \T K = 2-2 and for 

 the diurnal tides around IT 5. This means that: 



(1) if the Baltic is imagined to be closed in the south-west (the Baltic being 

 considered as a lake), the semi-diurnal tides, having very small amplitudes, 

 must have three nodal lines, the diurnal tides, with somewhat larger ampli- 

 tudes, one nodal line; 



(2) for the tides co-oscillating with the tides in the Danish waters, the 

 semi-diurnal tides must have two, the diurnal tides one nodal lines. 



Witting has computed the tides generated directly by the tide-generating 

 forces as listed under (1), as well as the transverse oscillations of this type 

 (periods of the free oscillation at about 2-5-5-5 h). The amplitudes of the 

 M % tide came to 0-6-0-9 cm, those of the K x tide to 3-4 cm. When the ratio 

 of the natural period to the period of the force is favourable, the amplitude 



