Linear Theories — Viscous 



TABLE 2 

 VoETiciTY Tendencies in a Symmetrical Cikcuxation 



87 



ocean, where the frictional-vorticity tendency is very small. However, on 

 the western side, where the velocity and shear are great because of the 

 narrowness of the western meridional current, the frictional- and planetary- 

 vorticity tendencies are greatly enhanced, to orders of magnitude greater 

 than that of the tendency of wind-stress vorticity, say +10 and —10 

 respectively. In this way we may achieve a balance between the tendencies 

 in the western side of the ocean as well, and so obtain a steady state. Table 3 

 shows the balance of terms in an asymmetric circulation. 



TABLE 3 



Vorticity Tendencies in an Asymmetric Cibcui/Ation 



If one analyzes ocean currents in this quahtative manner for anticy clonic 

 and cyclonic wind systems in both hemispheres, he will find that the neces- 

 sary intensification of the ocean circulation is always on the western side 

 of the ocean. This simphfied analysis apphes only to the viscous theories 

 of the Gulf Stream discussed in this chapter, not to the nonhnear theory 

 presented in Chapter VIII. 



WESTWARD INTENSIFICATION 



In 1946, when I first began to study the North Atlantic circulation, Dr R. B. 

 Montgomery suggested to me that the marked east-west asymmetry of the 

 surface circulation was one of the main features requiring explanation. 

 Soon afterward, I proposed a simple model of a wind-driven ocean 



