Wednesday, August 18, 2010

The Atmospheric Layer

Troposphere
It is the layer where they occur almost every weather and contains 80% of the total gas mass and 99% of water vapor the air of the troposphere is heated by the earth's surface and has a global average temperature of 15 ° C sea level, which decreases with altitude (on average 0.65 ° C per 100m above sea level) down to about -60 ° C to the tropopause. The air of the lower layers, which tends to rise, generating large convection currents giving rise to constant equatorial winds (trade winds) and atmospheric disturbances. The troposphere has a variable thickness depending on the latitude: the poles is only 8 km thick and reaches 17 km at the equator. The atmospheric pressure decreases with altitude according to an exponential law as a first approximation, beyond the 7-8 km altitude the pressure is so low that you can not breathe without the use of masks connected to oxygen tanks.

Climbing upwards, as well as pressure and temperature, also decreases the water vapor content of air. At one point the temperature stabilizes at -60 ° C. It is the tropopause, the transition zone between the troposphere and stratosphere.

The troposphere is derived from the greek word "tropos" meaning 'change', 'change' because within this sphere are all those horizontal and vertical movements of air that stir the atmosphere itself and that characterize the changing 'time air '. The troposphere is also the place of life than the weather: all plants and all living things live in it using some of its constituent gases.

Stratosphere
It is the atmospheric layer that lies above the troposphere and reaches a height of 50-60 km. Here is a phenomenon called temperature inversion: that is, while in the troposphere temperature decreases with height in the stratosphere increases up to 0 ° C. This phenomenon is due to the presence of an ozone layer (triatomic oxygen molecule), the ozone layer, which absorbs most solar UV radiation (approximately 99%). In some places the ozone layer has thinned ozone (ozone hole phenomenon, discovered in Antarctica) to the point that no longer offers effective protection against ultraviolet (UV) that under these conditions, can to reach land. These rays cause serious damage to plants and all living beings. The damage to humans may be skin cancer and blindness due to irreversible damage to the retina. Stratospheric components are increasingly rare, water vapor and dust fall, there are still some rare meteorological phenomena and certain specific types of clouds (cirrus).



Source: http://it.wikipedia.org/wiki/Atmosfera_terrestre


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