THE ATMOSPHERE, WEATHER, AND CLIMATE 



11 



respiration. Both plants and animals at various times 

 contribute some water vapor from their bodies to the 

 atmosphere. Furthermore, organisms, in eliminating 

 wastes and in decomposing after death, release some 

 form of nitrogen to the ground and, secondarily, to 

 the air. 



Contribution to the atmosphere by nonliving things 

 is a more complex procedure. Volcanoes emit water 

 vapor, carbon dioxide, and nitrogen, chiefly in the 

 form of ammonia. Lightning causes water vapor to 

 be broken down into its basic components, hydrogen 

 and oxygen, and ammonia to be broken down into 

 nitrogen and hydrogen. Atmospheric -storms also 

 activate some of the free ammonia so that it can enter 

 into the so-called nitrogen cycle. In this cycle, certain 

 bacteria cause chemical changes (involving the addi- 

 tion of oxygen to the nitrogen) to produce compounds 

 plants can use. These nitrogen compounds are used 

 in the complex food-producing activities of plants be- 

 yond the simple sugar production of photosynthesis. 



The land is a reservoir for atmospheric components 

 or products of these components. However, rocks and 

 soils contain free air as well as nitrogen compounds 

 that can be assimilated by plants. Another major air 

 reservoir is water. The various atmospheric gases are 

 in water. So are the products of the basic air com- 

 ponents, especially nitrogen compounds. Of course, 

 water also provides the air with water vapor. In fact, 

 evaporation from bodies of water is now the primary 

 source of atmospheric water vapor. 



The atmospheric cycle is only one of the many phe- 

 nomena that are collectively called bwgeochermcal cycles. 

 Each of the single cycles emphasizes the close inter- 

 relationship that exists between biological and physi- 

 cal phenomena. Moreover, each cycle is dynamic be- 

 cause it is dependent upon the interaction of many 

 separate factors that bring about a condition of equi- 

 librium. Because so many factors are involved, the 

 equilibrium of none of the cytles is definitely fixed; if 

 individual factors change, the condition of equilib- 

 rium will also change. Such an equilibrium change 

 might occur in the atmosphere, because man is affect- 

 ing certain of the separate factors. For example, man 

 is releasing more carbon dioxide, impurities (smog), 

 and radiation than normal. If these additions become 

 sufficient, they can lead to a new equilibrium, one 

 that will modify conditions for life on earth. There- 

 fore, the atmospheric cycle and all other biogeochemi- 

 cal cycles constitute natural resources that man must 

 conserve. 



ATMOSPHERIC GASES 



Many different gases are found in the atmosphere, 

 but only a few are found in significant concentra- 

 tions. The main gases and their approximate con- 

 centrations at sea level are: nitrogen, 78 per cent; 

 oxygen, 21 per cent; argon, 1 per cent; water vapor, 

 0.01 to 4 per cent; and carbon dioxide, 0.03 per cent. 



Atmospheric gases are extremely important. If it 

 were not for them, our planet's life, with the excep- 

 tion of a few kinds of bacteria, would not exist. How- 

 ever, the individual air components are not as im- 

 portant as is the insulating action of the entire atmos- 

 phere. If there were no gaseous envelope, the earth's 

 surface temperature would range from — 230°F. in 

 the shade to 300° F. in the sunlight. In addition, our 

 planet would have no fire, sound, weather changes, 

 sunsets, blue skies, or auroras. 



ATMOSPHERIC ZONATION 



The atmosphere has five zones, each characterized 

 by certain features. The troposphere (0 to 10 miles up) 

 contains 75 per cent of the air. It is about 5 miles 

 thick at the poles and 1 U miles thick at the equator. 

 Within the troposphere are clouds, as well as air 

 movement and weather changes. The tropopause is a 

 narrow transition area (not a zone) between the 

 troposphere and the stratosphere. The tropopause 

 has breaks that give it an overlapping, leaflike struc- 

 ture. The breaks give rise to the jet streams where 

 cold northern air meets warm southern air. The three 

 North American jet streams (the Canadian, Ameri- 

 can, and Subtropical) generally blow from the west 

 and are about 4 miles high and 300 miles wide. They 

 occur at ahitudes of 20,000 to 40,000 feet and move 

 at speeds of 50 to 300 miles per hour. Their names 

 imply the general areas through which each moves. 



The stratosphere (10 to 20 miles at our latitude) is 

 also an area of air movement. Furthermore, it is in 

 the stratosphere that solar ultraviolet light changes 

 oxygen to ozone. Although ozone is a poisonous, 

 gaseous combination of three oxygen atoms, it does 

 filter lethal ultraviolet light so that only enough 

 reaches the earth's surface to cause sunburn, to pro- 

 duce vitamin D, and to kill many bacteria. 



The chemosphere (20 to 40 miles) is the area where 

 airglow (a faint glow of air particles visible on clear 

 moonless nights) begins. 



The ionosphere (40 to 220 miles) is actually three 



