574 



Basic Principles of the General Oceanic Circulation 



EVAPORATION 



PRECIPITATION 



Fig. 262. The steady circulation of Goldsbrough type driven by precipitation over one-half 

 of a hemisphere and evaporation over the other half. Only one hemisphere has been pictured, 

 for the other hemisphere applies the reflected image. The curved lines with attached arrows 

 are isobars. The centres of high- and low-pressure cells are to the right resp. To the left of 



the middle line. 



subtropical and tropical regions. The geostrophic current will everywhere be directed 

 towards the equator in the precipitation hemisphere and towards the poles in the 

 evaporation hemisphere. The current towards the equator will require a horizontal 

 divergence, that towards the poles will require horizontal convergence. This diver- 

 gence (or convergence) distribution must be suflficient everywhere to absorb (or supply) 

 the water locally precipitated (or evaporated). 



The solution in Fig. 262 is valid for an entire hemisphere but it is evident that a 

 coastal barrier could be placed along any complete isobar without affecting the solu- 

 tion. Thus, meridional barriers can be placed tlirough the centres of the precipitation 

 and evaporation hemispheres, and also the equator itself can be selected as such a 

 barrier. 



This schematic representation of Goldsbrough's results has been discussed here in 

 some detail, since Stommel has used it as a basis for a discussion of the fundamental 

 principles of ocean circulation (see Chap. XXI). 



4. The Thermo-haline Circulation 



The general atmospheric circulation is produced solely by heat differences in 

 meridional direction, ultimately caused by the sun radiation. By analogy to the 



