Tides in the Mediterranean and Adjacent Seas 



397 



tante" ; at the narrowest point it attains at 6 h its maximum of nearly 

 200 cm/sec. Between 9 h and 3 h the current is directed southward, which 

 is called the "rema scendente" ; at h it has the same maximum value of 

 200 cm/sec. These currents computed theoretically can be compared with 

 observations made by Vercelli on an anchor station of 15 days in the cross- 

 section Punta Pezzo-Ganzirri, and which were submitted to the harmonic 

 analysis. He found the following surface values. 



Table 49. Harmonic constants of the tidal current 

 in the Strait of Messina 



{H in cm/sec, reduced to the transit of moon through the meridian in central European time.) 



In the lower layers down to the bottom the phase is almost constant, but 

 the velocity decreases slightly. The mean phase of the entire tidal current 

 is approximately 4-7 h, its intensity around 200 cm/sec. The theory gave 

 5 9 h, so that the observations show a priming of 1 2 h. It can certainly be 

 attributed partly to the friction on the rough ocean bottom and partly to 

 the strong turbulent mixing of the Tyrrhenian and Ionian Sea which takes 

 place in the narrowest section of the straits. In a very narrow canal, where 

 the compensation between the different levels on the surface takes place like 

 a river, the phase of these currents should be about 2-9 h. In the case of 

 a very wide canal, on the contrary, the tide would flow undisturbed and, 

 according to the theory, its phase would be 5-9 h. The actual case probably 

 lies between these two extremes; the average is 4-4 h, which is very close to 

 the observed "Value. Using the observed phases, we obtain along the strait 

 the average current conditions represented graphically in Fig. 168. Naturally, 

 the three-dimensional distribution over the entire cross-section of the strait 

 will be much more complicated. In the section after the sharp bend of the 

 strait to the north-east between Punta Pezzo-Ganzirri and C. Peloro-Scilla 

 we notice the occurrence of stream convergences, for the first time between 

 2\ h and 4 h when the current turns from north to south, the second time 

 between 6h h and 8 h when the current changes from south to north. These 

 stream convergences must be the seat and the source of current disturbances, 

 whose turbulent nature is still increased by the meeting of the two different 

 bodies of water which are never in equilibrium next to each other. The 

 Ionian water coming from the south is more saline and therefore heavier 

 than the water coming from the Tyrrhenian Sea which is lighter. This is 

 the point where eddies with vertical and horizontal axes develop and which 



