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1、Like a fish in the ocean, man is confined to a very shallow layer of atmosphere.The gaseous envelope of the Earth is physically inhomogeneous in both the vertical and horizontal directions, although the horizontal inhomogeneity is much less marked than the vertical inhomogeneity. Various criteria ha
2、ve been devised for dividing the atmosphere into layers. This division can be based on the nature of the vertical temperature profile, on the gaseous composition of the air at different altitudes, and the effect of the atmosphere on aircraft at different altitudes, etc. The division based on the var
3、iation of the air temperature with altitude is used most commonly in the meteorological literature. According to a publication of the agrological commission of the World Meteorological Organization (WMO) in 1961, the Earths atmosphere, is divided into five main layers: the troposphere, the stratosph
4、ere, the mesosphere, the thermosphere and the exosphere. These layers are bounded by four thin transition regions: the tropospause, the stratospause, the mesospause, the thermospause . The troposphere is the lower layer of the atmosphere between the Earths surface and the tropopause. The temperature
5、 drops with increasing height in the troposphere, at a mean rate of 6.5 per kilometer (lapse rate). The upper boundary of the troposphere lies at a height of approximately 8 to 12 km in the polar and troposphere contains about 75% of the total mass of atmospheric air, while in the tropics it contain
6、s about 90%. The tropoause is an intermediate layer in which either a temperature in version or an isothermal temperature distribution is observed. The stratosphere is the atmospheric layer above the troposphere. In the stratosphere the temperature either increases with height or remains nearly cons
7、tant. In the lower part of the stratosphere (up to approximately 20 km above the Earths surface) the temperature is practically constant (about 56 ). While further up the temperature increases with altitude at a rate of about 1 /km at heights of 20 to 30 km and about 2.8 /km at altitudes from 32 to
8、47 km. Under the standard conditions the temperature at the 47 km level is normally -2.5 . This increase in temperature with height is due to the absorption of UV solar radiation by ozone molecules. It should be noted that about 99% of the total mass of atmospheric air is concentrated in the troposp
9、here and stratosphere, which extend up to an latitude of 30 or 35 km. The stratopause is an intermediate layer between the stratosphere and the mesosphere (in the altitude region from 47 to 52 km ), in which the temperature remains constant at about 0.The thermosphere is the atmospheric layer above
10、the mesopause. The temperature in this layer increases with increasing altitude, reaching about 2000 at about 450km, the mean height of the upper boundary of the thermosphere. The temperature increase in this layer is mainly caused by the absorption of UV solar radiation by oxygen molecules, which d
11、issociate as a result of this.The exosphere is the furthest out and the least studied part of the upper atmosphere. It is located above 450km altitude. The air density in the exosphere is so low that atoms and molecules can escape from it into interplanetary space.Finally, along with the above divis
12、ion of the atmosphere, we will also make use of a division based on the extent of atmospheric interaction with the Earths surface. According to this principe,the atmosphere is usually divided into a so called boundary layer (sometimes also called the friction layer) and the free atmosphere. The atmo
13、spheric boundary layer(up to 1 or 1.5 km) is influenced considerably by the Earths surface and by eddy-viscosity forces. At the same time, we can neglect, as a first approximation, the influence of eddy-viscosity forces in the free atmosphere.Of all the above atmospheric layers, only the troposphere
14、(especially its boundary layer) is characterized by a marked instability of the vertical distribution of the meteorological parameters. It is in this layer that both temperature inversions and superadiabatic temperature variations with height are observed.The Earths atmosphere is a mixture of gases
15、and aerosols, the latter being the name given to a system comprised of small liquid and solid particles distributed in the air. Air is not a specific gas :rather, it is a mixture of many gases. Some of them, such as nitrogen, oxygen, argon, neon, and so on, may be regarded as permanent atmospheric c
16、omponents that remain in fixed proportions to the total gas volume. Other constituents such as water vapor, carbon dioxide, and ozone vary in quantity from place to place and form time to time. The principal sources of nitrogen, the most abundant constituent of air, are decaying from agricultural debris, animal matter, and volcanic eruption. On the other side of the ledger, nitrogen is removed from the atmosphere by biological processe
