The Tropospheric Circulation 



599 



Evidence against this conception of the equatorial counter current as a pure 

 gradient current has been accumulated by Sverdrup (1947) and Reid (1948), who 

 showed that the main features of the baroclinic mass distribution in the tropical and 

 subtropical Eastern Pacific are due entirely to the effects of the mean wind stress 

 distribution in these regions. A method for the determination of the mass field and 

 the mass transport of the currents from the given wind field has already been described 

 on p. 550 and following pages. By means of Fig. 254 it has been demonstrated that the 

 mass structure and the currents of the equatorial region of the Eastern Pacific are only 

 effects of the wind stresses. In these investigations full account was taken of the 

 dependence of the Coriolis parameter on the latitude, but the influence of lateral 

 friction and of thermodynamic effects such as radiation and evaporation and others 

 was neglected. The good agreement between theory and observations is an indication 

 that the latter effects are of secondary importance in the dynamics of the equatorial 

 counter current. Figure 273 presents diagrams of forces for the equatorial currents and 



Coriolis force 



Wind stress 



(b) 



Wind stress 



(c) 



Pressure grodient Windstress 



Pressure gradient 



Pressure yadient 



Equatorial 



Counter current 



Coriolis force 



Coriolis force 



Fig. 273. Diagrams of forces: {a) for the North Equatorial Current; {b) for the South 

 Equatorial Current; (c) for the Equatorial Counter Current. 



for the counter current. Basically there is no difference between them; since they are 

 each produced and maintained primarily by the wind in a sea with a baroclinic mass 

 structure. 



A comprehensive representation of the oceanic structure and circulation in a section 

 along the middle axis of the Atlantic is contained schematically in Fig. 274. It is self- 

 evident that this picture is of a schematic nature only, however, an attempt has been 

 made to include all the characteristic features of the tropospheric oceanic structure as 

 well as the corresponding three-dimensional circulatory movements. This circulation 

 in its zonal extent is largely a consequence of the air currents over the sea surface. The 



