AEROGRAPHER'S MATE 3 & 2 



Layers of the Atmosphere 



The layers and 

 under two separate 

 METEOROLOGICAL 

 zones according to 

 weather, and the 

 classification which 

 electrical characte 

 atmosphere. 



zones will be discussed 

 classifications. One is the 

 classification which defines 

 their significance for the 



other is the ELECTRICAL 

 defines zones according to 



ristics of gases of the 



METEOROLOGICAL CLASSIFICATION. — In 

 the meteorological classification (commencing 

 with the earth's surface and proceeding upward) 

 are encountered the troposphere, tropopause, 

 stratosphere, stratopause, mesosphere, meso- 

 pause, thermosphere, and the exosphere. These 

 classifications are based on temperature 

 characteristics. 



Troposphere. — The troposphere is the layer 

 of air enveloping the earth immediately above 

 the earth's surface. It is approximately 5 1/2 

 miles (29,000 ft or 9 km) thick over the poles, 

 about 7 1/2 miles (40,000 ft or 12.5 km) thick 

 in the mid-latitudes, and about 11 1/2 miles 

 (61,000 ft or 19 km) thick over the Equator. 

 The figures for thickness are average figures, 

 they change somewhat from day to day and 

 from season to season. The troposphere is 

 thicker in summer than in winter and is thicker 

 during the day than during the night. All 

 weather, as we know it, occurs in the troposphere. 



The troposphere is composed of a mixture 

 of several different gases^ By volume, the 

 composition of dry air in the troposphere is 

 as follows: 78 percent nitrogen, 21 percent 

 oxygen, nearly 1 percent argon, and about 0.03 

 percent carbon dioxide. In addition, it contains 

 minute traces of other gases, such as helium, 

 hydrogen, neon, krypton, and others. 



The air in the troposphere also contains a 

 variable amount of water vapor. The maximum 

 amount of water vapor that the air can hold 

 depends on the temperature of the air and the 

 pressure; that is, the higher the temperature, 

 the more water vapor it can hold at a given 

 pressure. 



The air also contains variable amounts of 

 impurities, such as dust, salt particles, soot, 

 and chemicals. There impurities in the air are 

 important because of their effect on visibility 

 and especially because of the part they play in 

 the condensation of water vapor. If the air were 



absolutely pure, there would be little condensa- 

 tion; these minute particles act as nuclei for 

 the condensation of water vapor. Nuclei which 

 have an affinity for water vapor are called 

 HYGROSCOPIC NUCLEI. 



The temperature in the troposphere usually 

 decreases with height, but there may be inversions 

 for relatively thin layers at any level. 



Tropopause. — The tropopause is a transition 

 layer between the troposphere and the strato- 

 sphere. It is not uniformly thick, and it is not 

 continuous from the Equator to the poles. In 

 each hemisphere the existence of three distinct 

 tropopause s is generally agreed upon — one in 

 the subtropical latitudes, one in middle lati- 

 tudes, and one in subpolar latitudes. These 

 may overlap or may be folded. 



The tropopause is characterized by little 

 or no increase or decrease of temperature 

 with increasing altitude. The composition of gases 

 is about the same as that for the troposphere. 

 However, water vapor is found only in very 

 minute quantities at the tropopause and above it. 



Stratosphere. — The stratosphere directly 

 overlies the tropopause and extends to about 

 30 miles (160,000 ft). Temperature varies little 

 with height in the stratosphere through the first 

 30,000 feet; however, in the upper portion the 

 temperature increases approximately linearly to 

 values nearly equal to surface temperatures. 

 This increase in temperature through this zone 

 is attributed to the presence of ozone which 

 absorbs most of the incoming ultraviolet 

 radiation. 



Stratopause. — The stratopause is the top of 

 the stratosphere. It is the zone marking another 

 reversal of temperature with increasing altitude. 



Mesosphere. — The mesosphere is a layer 

 approximately 20 miles (100,000 ft) thick which 

 directly overlies the stratopause. The tempera- 

 ture decreases with height. 



Mesopause. — The mesopause is the thin 

 boundary zone between the mesosphere and the 

 thermosphere. It is marked by a reversal of 

 temperature; i.e., temperature again increases 

 with altitude. 



Thermosphere. — The thermosphere, a second 

 region in which the temperature increases with 

 height, extends from the mesopause to outer 

 space. 



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