transformed to a motional form other than heat. In fact, motion is 

 produced only as a consequence of heating or cooling which supplies 

 mechanical energy by 1) evaporating water over large areas of the ocean 

 so that a return flow from other areas is induced, 2) increasing the 

 salinity or density of surface waters which then tend to sink, and 

 3j heating surface waters so that they expand above the equilibrium 

 water level and gain potential energy. 



The importance of a given process depends on the season (S, 122). 

 At 47®N, 12°W, for instance, most evaporation takes place from September 

 to November and the latent heat is supplied more from the thermal energy 

 stored during the summer months than from solar heating at the time. 



To estimate the magnitude of the mechanical energy that could be 

 obtained as a result of evaporation, assume that steady evaporation has 

 lowered the depth of the ocean over a large area by the amount h and 

 raised the level by precipitation in another area by a similar amount. 

 Water flowing from the high areas to the low would then lose potential 

 or gain kinetic energy at the rate 



2 h p g -TT = 4o8xl0~ h ergs cm" sec" . 



The quantities p and g are the density of sea water and the acceler- 

 ation of gravity respectively. Substitution of these values and the value 

 for the evaporation rate — , of 2.9xl0" cm sec" per unit area of ocean 

 into the above expression yields the quantity on the right of the equation. 



The evaporation rate was determined from the annual rate of evaporation 



3 3 -1 

 over all oceans, 334x10 km yr (S, 120), The kinetic energy gained in 



-7- 



