468 Water Bodies and Stationary Current Conditions at Boundary Surfaces 



rotational (cyclonic or anticyclonic) motion. The anticyclonic winds around the sub- 

 tropical high-pressure centres thus give rise in both hemispheres to anticyclonic large- 

 scale vortices between the oceanic West Wind Drift and the Equatorial Currents. 

 These are elongated corresponding to the shape of the high-pressure cells and take the 

 form of a broad convergence zone. In the central parts of these anticyclonic vortices 

 there is always a mass distribution corresponding to that in Fig. 211 b; that is, with 

 an accumulation of lighter water in the central part of the convergence area. Condi- 

 tions of this type are particularly well developed in the North Atlantic, where there is 

 an accumulation of warmer water with a corresponding depression of the isosteres to 

 600-800 m ; the isobaric surfaces and the physical sea level show a corresponding 

 uphft. 



Large-scale vortices with cyclonic sense of rotation are found in the intermediate 

 region between the oceanic West Wind Drifts and the Polar Currents; that in the 

 North Atlantic between the Polar and the Atlantic Current. Here the actual oceanic 

 structure will be very nearly that pictured in Fig. 2\l a, which shows that the isosteres 

 arch upwards. Such cases will be referred to again when discussing the current con- 

 ditions in particular oceanic regions, 



A very typical case of a smaller-size cyclonic vortex was observed in the Gulf 

 Stream just north of the Azores above the "Altair" cone during the International 

 Gulf Stream Survey, 1938 (Defant, 1940 b). The centre of the vortex was found in 

 upper layers a little south of the greatest submarine elevation; in deeper layers it 

 appeared directly above the cone. All the vertical oceanographic sections show this 

 vortical disturbance and its vertical structure. Figure 212 presents a somewhat smoothed 



100 



200 



300 



E 400 



500 



600 



700 



800 



900 



Fig. 212. Meridional density section through the cyclonic vortex above the "Altair' 

 submarine volcano in the Atlantic Ocean (somewhat smoothed). 



