DISTRIBUTION OF SALINITY, TEMPERATURE, DENSITY 



75 



at any season. The larger displacements are all in regions in which the 

 surface currents change during the year because of changes in the pre- 

 vailing winds, and this feature also is therefore closely associated with 

 the character of the atmospheric circulation. The surface temperatures 

 in the Southern Hemisphere are generally somewhat lower than those in 

 the Northern Hemisphere, and again the difference can be ascribed to 

 difference in the character of the prevailing winds, and perhaps also to a 

 wide-spread effect of the cold, glacier-covered Antarctic Continent. 



Table 11 



AVERAGE SURFACE TEMPERATURE OF THE OCEANS BETWEEN 

 PARALLELS OF LATITUDE 



The average distribution of the surface temperature of the oceans in 

 February and August is shown in charts 1 and 2. Again the distri- 

 bution is so closely related to the formation of the different water masses 

 and the character of the currents that a discussion of the details must be 

 postponed. 



Difference Between Air- and Sea-Surface Temperatures. It 

 was pointed out that in all latitudes the ice-free oceans received a surplus 

 of radiation, and that therefore in all latitudes heat is given off from the 

 ocean to the atmosphere in the form of sensible heat or latent heat of 

 water vapor. The sea-surface temperature must therefore, on an 

 average, be higher than the air temperature. Observations at sea have 

 shown that such is the case, and from careful determinations of air tem- 

 peratures over the oceans it has furthermore been concluded that the 

 difference, air- minus sea-surface temperature, is greater than that derived 

 from routine ships' observations. In order to obtain an exact value, it is 

 necessary to measure the air temperature on the windward side of the 

 vessel at a locality where no eddies prevail and where the air reaches the 

 thermometer without having passed over any part of the vessel. For 

 measurements of the temperature a ventilated thermometer must be 

 used. According to the Meteor observations the air temperature over 

 the South Atlantic Ocean between latitudes 55°S and 20°N is, on an 

 average, 0.8° lower than that of the surface, whereas in the same region 



