CLIMATIC FACTORS : THE AIR 



89 



is more apt to result from the slow ascent of warm air currents 

 along atmospheric fronts or great shifting air masses. In the vicinity 

 of mountains the same effect is obtained by moist air being forced 

 upward to altitudes of lower temperature and density. The high- 

 est precipitation records are usually found on windward slopes of 

 mountains and are produced by such forced ascents of air. Tropi- 

 cal rains, although often very heavy, are usually convectional in 

 origin. 



FlG. 36. Coastal redwood forest in California, showing the characteristic 

 morning fog that is a factor in its survival.— U. S. Forest Service. 



