DISTRIBUTION OF SALINITY, TEMPERATURE, DENSITY 



77 



computation of the average temperature of the air between latitudes 20®N 

 and 80°N along the meridian of 120°E, which runs entirely over land, and 

 along the meridian of 20°W, which runs entirely over the ocean. In 

 January the average temperature along the ''land meridian '^ of 120°E is 

 - 15.9^ but along the "water meridian" of 20°W it is 6.3°. In July the 

 corresponding values are 19.4° and 14.6°, respectively. Thus in January 

 the air temperature between 20°N and 80°N over the water meridian 

 is 22.2° higher than that over the land meridian, whereas in July it is 4.8° 

 lower. The mean annual temperature is 7.0° higher along the water 

 meridian. 



Cf 60* N 



Fig. 16. Average annual ranges of surface temperature in the different oceans 

 plotted against latitude (heavy curves) and the corresponding ranges in the radiation 

 income (light curves). 



Annual Variation of Surface Temperature. The annual varia- 

 tion of surface temperature in any region depends upon a number of 

 factors, foremost among which are the variation during the year of the 

 radiation income and the character of the ocean currents and of the 

 prevailing winds. The character of the annual variation of the surface 

 temperature changes from one locality to another, but a few of the general 

 features can be pointed out. The heavy curves in fig. 16 show the 

 average range of the surface temperature in different latitudes in the 

 Atlantic, the Indian, and the Pacific Oceans. The range represents 

 the difference between the average temperatures in February and August, 

 and the thin lines in the same figure show the range of the radiation 

 income. The curves bring out two characteristic features. In the first 

 place, they show that the annual range of surface temperature is much 



