396 



Tides in the Mediterranean and Adjacent Seas 



down till 30 depth and from this depth to the bottom at about 106 m in 

 a northward direction corresponding to the vertical density distribution of 

 the Tyrrhenian Sea in the north and of the Ionian Sea in the south (see 

 vol. 1/2). Their velocities in both layers are of the order of magnitude of 

 10 cm/sec, but can increase to considerably greater values, through wind 

 and piling up effects. Superposed on these stationary currents are the tidal 

 currents originating from the co-oscillation of the water-masses of the strait 

 with the tides of the adjacent seas. As we have seen, these tides have a nearly 

 opposite phase with equal amplitudes, i.e. when the Ionian Sea off the strait 

 has high water, then the Tyrrhenian Sea has low water and inversely. If the 

 tides at the opening of the strait in the north and the south are known, the 

 tides and the tidal currents within the strait can be computed according to 

 the method of the step-wise integration of the equations of motion (p. 339), 

 taking into consideration the morphologic conditions of the connecting canal. 

 If at first, the frictional influences are neglected we obtain the picture as 

 represented in Fig. 167. The tides of the area of the strait south of the nar- 



Fig. 167. Phase and amplitude of the tide in the Messina Straits. --«--, intensity of the 

 tidal current (friction neglected). 



rowest cross-section (Punta Pezzo-Ganzirri) behave essentially like the Ionian 

 Sea, except that the amplitude of the tide gradually decreases to zero ap- 

 proaching the first location. The same applies for the section north of this 

 cross-section, which is governed by the tides of the Tyrrhenian Sea. Within 

 a very short distance of a little more than 3 km, the phase of the tide varies 

 by nearly 6 h. At this point occur the greatest slopes of the sea surface. 

 At 3 h the difference in elevation of the sea surface over this short distance 

 is 1-7 cm/km from south to north At 9 h it is reversed from north to south 

 and at h and 6 h the surface is nearly level. The velocities of the current 

 related with the maximum gradients are shown in the figure: between 3h 

 and 9h the current is directed northward; this is the so-called "rema mon- 



