Basic Principles of the General Oceanic Circulation 



583 



If the absolute numerical values of the three vorticity terms in (XVII. 5) are denoted 

 by a, b and c, then for a symmetrical wind system, {a) would be negative and would 

 have the same numerical value in both east and west. For an equal velocity, a sym- 

 metrical oceanic circulation would require an equally great frictional vorticity; 

 (Jb) would thus be positive and have the same numerical value in the east as in the 

 west. The planetary vorticities in the west and in the east would also have the same 

 numerical value but are of opposite signs. Thus 



Off the western boundary 

 — « + Z7 - c =0 



Off the eastern boundary 

 — a + Z) + c =0 



These requirements are satisfied only when c = 0, that is, when there is no meridional 

 transport, and are therefore incompatible with the conservation of mass. This is a 

 qualitative explanation 



(1) of the impossibility of a symmetrical circulation in association with a sym- 

 metrical wind field, 



(2) of the impossibility, mentioned above, of deriving a suitable circulation off the 

 western coast of an ocean without accounting for frictional influences. 



As shown by Stommel, an anticyclonic circulation is possible in the case just 

 discussed only when the water transport off the western boundary is substantially 

 intensified and the lateral shearing stresses consequently, of course, increased corres- 

 pondingly. To illustrate this, Stommel gives some arbitrary values for the vorticity 

 terms in an asymmetric circulation. These are shown in the following Table 149. 



Table 149. Vorticity tendencies in an asymmetric 

 circulation 



Among the interesting consequences of this theory are : 



(1) the fact that although energy is added to the oceans by work done by the wind 

 over the entire surface, it is dissipated primarily in the strong western currents ; 



(2) that a good representation of the circulation in the zonal currents of westward 

 or eastward direction can be obtained independently of friction from a know- 

 ledge of the wind stress field alone. 



MuNK (1950) was able to evolve a comprehensive theory of a wind-driven ocean 

 circulation by combining three new concepts : 

 (fl) the introduction of lateral stresses associated with the horizontal exchange in 



large eddies (Defant, 1926; Rossby, 1936a), 

 (6) the possibility of computing currents in baroclinic oceans from the known 



wind stresses (Sverdrup, 1947), and 



