490 



Ocean Currents in a Non-homogeneous Ocean 



somewhat wider sense. In the real ocean differences in specific volume are produced 

 not only by h,eat gain or heat loss, that means thermally, but also by changes in salinity. 

 Evaporation will increase salinity and precipitation, ice melting and the inflow of 

 fresh water (run-off) will reduce it. An increase in salinity has the same effect as a 

 cold source and a decrease in salinity will be equivalent to a heat source. In the 

 following the sources of heat and cold will be taken as including always the combined 

 effects of both factors. 



In a Camot cycle one single and complete revolution shall now be considered on an 

 [a,/j] -diagram (Fig. 224) consisting of two isobars {dp = 0) and of two adiabatic 

 curves along which there is no addition or removal of heat and changes will occur only 

 due to expansion or contraction. There are two possible cases: 



Fig. 224. Camot's cycle. Case o: heat source at lower pressure (small ocean depth) than cold 



source. Case b: heat source at higher pressure (great ocean depth) than cold source. A 



stationary circulation is only possible in case b, not in case a. 



(a) Clockwise cyclic process. From 1 to 2 at a constant, but lower pressure {p^ < p^, 

 in the upper part of the sea) there will be a heat input (heat source), from 2 to 3 there 

 will be an adiabatic compression followed from 3 to 4 by a heat removal (cold source) 

 at higher pressure (in the lower part of the sea). Finally, an adiabatic expansion occurs 

 from 4 to 1. Evaluation of the integral (XV. 15) gives, since the isobaric sections of the 

 cycle make no contribution 



a dp = \ (a 



a4.i) (ip > 0» 



f, 



since both (02,3 — 04,^) as well as dp are greater than zero. The pressure forces are 

 incapable to do work. Any existing circulation will in time be destroyed by frictional 

 effects. 



(b) Counter-clockwise cyclic process. The heat source works at high pressure 



I < P2, in the lower part of the sea). 



In this case 



a dp 



(04,1 — aa.a) dp < 0. 



The pressure forces are capable to do work. If this is so large as to overcome all the 

 frictional forces there will be a steady circulation. 



If there were no friction, this would be a reversible process and the degree of 

 efficiency of this thermodynamic machine would be given by W = {Q^ — Q-^iQi, 

 where Q^ is the amount of heat absorbed by the medium from its surroundings at the 



