472 Water Bodies and Stationary Current Conditions at Boundary Surfaces 



conditions, the West Wind Drift must have a greater velocity towards the east than the 

 South Polar Current to the south of it, which is also directed east. Since here also 

 disturbed meteorological conditions are frequent in this region, the varying influence 

 of the action of the atmospheric flow will sometimes accelerate the oceanic West 

 Wind Drift and sometimes the South Polar Current, and therefore the polar boundary 

 surface will change from an up-gliding to a down-gliding surface and back again and 

 there will be corresponding displacements of the polar front in meridional direction. 

 These processes seem to continue nearly all the time and may be associated with the 

 observed sinking process of large water quanta of sub-Antarctic waters. This process 

 is most probably of a pulsatory character and is definitely the source of the sub- 

 Antarctic intermediate water penetrating far to the north. 



Variations of the boundary surface can also arise in circular vortices if there are 

 changes in the vertical current structure. If (see in Fig. 215) for example, the boundary 



Fig. 215. Pulsations of a circular vortex in cyclonic rotation. 



surface and the physical sea level lie in the position 1-1 under average conditions, then, 

 if the velocity between the upper and lower water bodies increases, there will be greater 

 accumulation of the lower water type around the axis of the vortex and the inclination 

 of the boundary surface will increase (position 2-2). If, on the other hand, this diff"er- 

 ence becomes less, then the accumulation of lower water will be dispersed and the 

 inclination will decrease. Periodic variations in the mass structure will thus occur in 

 the vortex; the boundary surface and the physical sea level will oscillate ^round a 

 mean position and these oscillations will have the character of standing waves (see 

 Vol. II). 



In the cyclonic vortex over the "Altair" submarine cone in the Gulf Stream north 

 of the Azores (see p. 454) periodic variations of this type were present both in the oceanic 

 structure and in the vertical current distribution. They were very well developed in the 

 upper system and of a period corresponding to the inertia period (17 n). Since the 

 periodic variations in the current amounted to as much as half of the velocity of the 



