142 



ANALYSIS OF THE ENVIRONMENT 



bottom, particularly in the higher latitudes. 

 The distribution of the masses of land and 

 water and the topography of the land, 

 among other things, also distmrb the simple 

 working of the diagrammatic planetary pat- 

 tern for winds especially in the lower at- 

 mosphere and more especially over the con- 

 tinents. The world systems of winds and 

 of ocean currents have much in common 



in which the air is mixed by convection 

 currents and in which temperature de- 

 creases with increasing height. Above the 

 troposphere is the stratosphere, in which 

 convection currents are lacking and in 

 which temperature, when not independent 

 of altitude, becomes higher with increasing 

 distance above the earth. Above the strato- 

 sphere, at an altitude of almost 50 miles, 



High 



^"^^^'Le OF UPPt^ '''^ 



Fig. 26. Schematic diagram of the planetary circulation. ( Redrawn after Osbom. ) 



and interact closely on each other. It will be 

 helpful to consider the winds first, not as 

 entities in themselves, as meteorologists do, 

 but in their ecological relations, and later 

 to turn to a similar, brief discussion of 

 ocean currents. 



THE ATMOSPHERE 



The atmosphere has a more or less defi- 

 nite structure that is schematically summa- 

 rized in Figure 25. The portion nearest the 

 earth is called the troposphere. It extends 

 some 6 or 7 miles above sea level in tem- 

 perate latitudes and usually goes up 8 or 

 10 miles in the tropics. This is the region 



is the extremely tenuous ionosphere. Al- 

 though the atmosphere is composed of 

 "thin air," it weighs in all some 56,328 X 

 10^^ tons, and one of the large cyclonic 

 storms, characteristic of the temperate re- 

 gion, may cause the physical translocation 

 of five milhon-million tons of atmosphere. 



THE PLANETARY PATTERN OF THE \VINDS 



If the earth's surface were relatively 

 homogeneous and smooth, we would expect 

 to find an average planetary wind system 

 like that outlined in Figure 26. Some dis- 

 tance up, say about two and a half miles, 

 still well within the troposphere, the move- 



