398 



Tides in the Mediterranean and Adjacent Seas 



can acquire large dimensions. The circumstance that in this part of the strait 

 the upper water layer in its steady position travels southwards, whereas the 

 lower layer moves northwards, plus the tidal currents, contributes to the 

 development of dynamical instabilities, which dissolve into eddies. This is 

 substantiated by the observations. Around 3 h, when the "rema montante" 



Fig. 168. Average current for each lunar hour along the N. S. longitudinal axis of the 



Strait of Messina. 



starts, a disturbance of the current develops in the form of a bore called 

 "primo taglio della rema montante" near Ganzirri, which travels to C. Peloro 

 in 45 min. At 4 h there is a second wave in the vicinity of Torre Faro which 

 travels in 35 min to Scilla; this is called the "secondo taglio". According to 

 Vercelli, these waves are like a bore in estuaries (p. 464), the heavy water 

 of the Ionian Sea rushes head on against the slowly receding lighter water 

 of the Tyrrhenian Sea. 



The "rema scendente" is also accompanied by "tagli"; the first one, rather 

 weak, is formed near Pezzo at about 6| h to 7 h and travels up to Messina; 

 the second one, the largest, the "taglio grande", develops near C. Peloro 

 and travels southwards down the entire strait. The lighter Tyrrhenian water 

 glides rapidly over the heavier Ionian water in the form of a bore. The "tagli" 

 or "scale di mare", which are particularly important at the time of syzygies, 

 have been described extensively by Vercelli and Mazzarelli, to whose papers 

 the reader is referred. However, they develop into large-scale phenomena 

 when strong winds pile up one kind of water against the other. 



In connection with the convergences of currents, we must mention the 



