656 The Tropospheric Circulation 



The equation for w will become the same as in the earlier state and the vertical 

 velocity distribution will therefore remain unchanged throughout the whole period of 

 upwelling process as long as the wind is kept steady. During this period the ascending 

 water movement will be subject to mixing with the surrounding waters and the thermo- 

 line will not be raised to any large extent. From equation (XIX. 71) it follows that at 

 this stage the vorticity in the surface layer will be proportional to the vertical velocity. 

 Upwelling will thus be associated with cyclonic vorticity in contrast to the initial 

 inshore increase in negative vorticity produced by the coastal upwelling. This approach 

 developed by Yoshida undoubtedly appears to give a deeper insight into the dynamics 

 of the upwelling process, but a more specific representation in detail of these processes 

 would be desirable. 



5. Processes at the Polar Boundary of the Subtropical Convergence Region 



The subtropical convergence regions are oceanic areas where the oceanographic 

 factors show large local and time variations (p. 575). They can be interpreted as con- 

 sequences of vortex formations between the two somewhat different types of water on 

 the polar and the equatorial sides of the convergence region. On the one hand, there 

 are intrusions of warm highly saline water from lower towards higher latitudes, and on 

 the other hand, intrustions of cold and weakly saline water occur in the opposite 

 direction. All the isolines of the oceanographic factors and the isolines of the dynamic 

 topography of the pressure surfaces thus show a wave-like structure. Whether all the 

 deviations from a smooth curved pattern are of an aperiodic nature propagated in 

 one direction along the boundary region between the two water types and in time 

 dying out, cannot be decided without a rapid succession of synoptic surveys. Since 

 series-observations, made in the convergence region at quite different times, can all 

 be combined without excluding any large number of individual values into closed 

 comprehensive representations ; it may be safely concluded that the disturbances are 

 often quasi-stationary vortical disturbances whose position and extent are probably 

 determined by external factors. 



These wave-form disturbances are particularly well developed in the convergence 

 region of the South Atlantic. The topography of the physical sea level between 25° 

 and 50° S. (Fig. 308) shows the irregular wave-like patterns in the course of the dynamic 

 isobaths. This starts suddenly off the broad Patagonian-Argentinian shelf and extends 

 across the total width of the Atlantic to the region south of Africa. According to the 

 topographies of the deeper levels these wave-form disturbances reach down to con- 

 siderable depth but their intensity decreases rapidly with depth. They can hardly be 

 detected in the topography of the 1400-decibar surface. Their greatest intensity is 

 always found in the top layers where they must originate and therefore the reason for 

 their formation must be looked for here. The entire oceanic structure is shifted towards 

 the poles and the equator, respectively, by the interacting intrusions of different water 

 masses in a strip-like manner, and thereby differently stratified oceanic spaces oppose 

 each other side by side that would normally be found arranged in a zonal fashion. 

 Then inside the resultant vortical formations of both water types, heavier water sinks 

 down at the boundary surface extending to more southern latitudes, while the lighter 

 water at the same time is lifted and extends further towards the poles. The sinking 

 process of the heavier waters apparently does not take place everywhere along the 



