134 Temperature 



the year. At Quito, Ecuador, for example, the average seasonal 

 change is only 0.5°C. 



Horizontal Changes. The changes in temperature from place to 

 place over the surface of the globe run the whole gamut of extreme 

 values that have been reviewed. Average temperatures on land are 

 too variable for simple generalization, but a value of 32°C may serve 

 as an approximation for tropical regions and one of — 12°C for polar 

 regions. For detailed information a textbook on climatology should 

 be consulted, such as Kendrew ( 1949 ) . In the sea average tempera- 

 tures run from about 30°C in the tropics to about — 1.5°C in the Arctic 

 and Antarctic Oceans. 



Vertical Changes. The temperature of the air varies widely in a 

 vertical direction according to local conditions, but a decrease of 

 about 1°C for every 150 m of altitude is generally found. On Mt. 

 Washington in New Hampshire the tabulated average values were 

 obtained for observations from 1933 to 1940. 



Pinkham Notch (Altitude 610 m) 

 Summit (Altitude 1915 m) 



Difference: 6.4°C 7.2°C 7.0°C 



The unequal heating of the air horizontally and vertically causes 

 movements of the atmosphere. These are manifested as local winds, 

 trade winds, and storms with consequent further influence on tem- 

 perature, precipitation, and other ecological factors. 



Air is heated at all levels by the solar radiation that it absorbs and 

 similarly may cool at all levels, but the greatest amount of heating 

 and cooling takes place at the bottom. This effect is due to the great 

 transparency of the air and the fact that the surface of the earth is 

 heated faster during the day and cools by radiation more rapidly dur- 

 ing the night than the atmosphere. The air in immediate contact with 

 the earth therefore changes temperature more rapidly than strata at 

 greater altitudes. The easy mobility of the atmosphere also contrib- 

 utes to the thermal variations of the air environment. When air 

 overlying heated land masses becomes warm, it tends to rise and to 

 leave the earth's surface, but air chilled by contact with cold earth is 

 heavier and tends to accumulate in hollows of the landscape. In 

 these respects air stands in distinct contrast to the water environment 

 in which heating and cooling take place principally at the upper 

 surface. 



The spectral distribution of the energy received from the sun at the 



