Currents in a Strait 



531 







100 



E 200 



. 300 



1400 



500 



Mediterranean seo 





 100 



200 



E 



^- 300 



Q. 



Q 400 

 500 



7 



, . • Boundary between different 



,^ — water masses 



-^''"^_ r r /^ 



.■■' ^-^ . ~ Limit between currents 



\ of different (jirection 



Summer 



Fig. 245. Schematic representation of the water type and of the current Hmit in the inner 

 region of the Strait of Gibraltar (according to Schott). 



The few sporadic current measurements that have been made in the Strait of Gib- 

 rahar are in good agreement with the currents deduced from the longitudinal sections. 

 The upper current towards the east is particularly strong in the middle of the strait and 

 on its southern side. In the bays on both sides of the strait there are large vortical 

 movements ("neer" currents). The main current is considerably affected by wind and 

 tides and persistent easterly winds may even stop at time the inflow into the Medi- 

 terranean. The mean velocity of the upper current core according to Nares (1872) is 

 34 cm/sec ; ebb and flood superimpose the mean velocity and this results in a velocity 

 of +57 cm/sec giving an eastward flood current of 91 cm/sec and a westward ebb 

 current of 23 cm/sec. The currents are strongest along the southern edge of the deeper 

 southern channel and may reach as much as 210 cm/sec. The preference for the south- 

 em side, due to the Earth's rotation, can also be seen by means of the thermo-haline 

 cross-sections which show the Atlantic water of low salinity deflected to the right 

 along the African side. 



Measurements made by the "Michael Sars" expedition (Murray and Hjort, 1912, 

 p. 290) give the vertical current profile shown in Fig. 246. The current boundary lies 

 at a depth of 142 m. Equation (XVI. 13) allows a computation of the average down 

 slope of the physical sea level from the Altantic Ocean to the Mediterranean and one 

 obtains as an average value 0-6 cm in 100 km, while the current boundary surface 

 rises by about 15 m in 100 km. In spite of the simplifying assumptions in the theory 

 there is satisfactory agreement between observations and theory. Direct current 



