580 



Basic Principles of the General Oceanic Circulation 



mass, meridional currents must develop that will determine the nature of the circula- 

 tion. It appears that these boundary conditions are more easily fulfilled for a sea with 

 a meridionally oriented eastern coast than for one with a meridionally oriented 

 western coast. 



{a) Conditions West of a Meridionally Oriented Coast 



SvERDRUP (1947) has shown that a steady state solution can be found for a density- 

 layered ocean by starting at a meridional boundary and working westwards even when 

 frictional effects are neglected. In the vorticity equation (XVII. 5) the wind stress vort- 

 icity must be balanced by the planetary vorticity alone and, as shown already in XVII.3 

 second of the major boundaries of the oceanic circulation. To reach the surface at 

 the boundary conditions and the equation ofcontinuity(XVII.4) determine the currents 

 westward from the meridional boundary (east coast). For a purely zonal wind 

 {Ty = 0), the mass transports (omitting the first term of (XV1I.7) ; lower latitudes) 

 will be given by 



My = --^^' and M^^j-^. (XVIII.5) 



Assuming in a schematic way according to actual conditions in the ocean (equator 

 to 30°: easterly winds; 30° to 60°: westerly winds) 



T = 



a sm -r-y. 



(XVIII.6) 



where / is the distance from the equator until 60°, then 



-^.^-jT^^njy. 



From this it is easy to derive the following table of signs of the different quantities for 

 an eastern or western meridional barrier. 



Possible case 



Impossible case 



West of the barrier, T^ and M^ are, according to (XVIII.5), both positive or both nega- 

 tive. However, east of the barrier they are of opposite signs, which is impossible. 

 The equations (XVIII.5 and 6) give a steady state solution only for a sea area to the 

 west of the boundary. The foUov/ing example can be taken as an illustration of such a 

 solution. 

 Selecting T^ = — 0-4 sin 6(f> dyn cm"', gives 



M. 



2-4 

 2<x) cos (f> 



cos 6(f) ; Mx 



14-4 Zljc 

 2Rw cos <f> 



sin 6(f) and tfj = — 



2-4 Ax 



2co COS(f> 



cos 6(f). 



