Monday, March 7, 2011

Atmosphere


The atmosphere forms an insulting blanket around the earth. Without it the temperature at the equator would rise to 180 F during the day and drop as low as -220 F at night. It burns up meteors that would bombard the surface of the earth from space. Without the atmosphere there would be no sound and light. Without air there would be no lighting, no wind, no rain, no snow, and no fire.
The atmosphere shields the earth from lethal concentrations of ultraviolet radiation. It selectively filter’s the sun’s rays so that only two small segments of the electromagnetic spectrum penetrate to the earth’s surface in appreciable amounts. One segment is the optical window, consisting essentially of the visible spectrum of light, from near ultraviolet to near-infrared. The other is the radio window, consisting of radio waves from about 1 centimeter to 40 meters in length. There is no boundary between the atmosphere and the void ratio. However, 75% of the earth’s atmosphere lies within 10 miles of the surface and 99% of the atmosphere lies below an altitude of 30 kilometers. The total mass has been estimated at 5,500 trillion tons.

The zones of the atmosphere: There are four zones in the atmosphere. The description is given below:
  1.   Troposphere: The zone nearest the earth is troposphere, named from the Greek tropein (to turn, to rotate, and to change). One property that changes in the troposphere is the temperature. It drops to -55 c by the time an altitude of about 16-18 km is reached. The rate of temperature drop is about 6.4 c per 1000 meters, a figure called the normal environmental lapse rate. At the equator it is 18 kilometers thick and at the poles it is only 8 kilometers thick. Essentially all the atmosphere's water vapor is in the troposphere which therefore encloses all the storms and precipitation of the earth.
  2. Stratosphere: This zone starts at the top of the troposphere, at a thin atmospheric “shell” called the tropopause, where the temperature to stay fairly constant, increasing slightly, in going to an altitude of 50 kilometers. The stratosphere includes much of the ozone layer. The stratopause marks the narrow zone at the top of the stratosphere where the temperature begins to fall again with increasing altitude as the mesosphere is entered.
  3. Mesosphere: The mesosphere, on top of the stratosphere, extends roughly to 80 kilometers. Its temperature drops to between -80 and -90 c at the mesopause, a thin zone where the temperature stabilizes and soon starts to rise again as the thermosphere is ascended.
  4.  Thermosphere: This zone is above 80 kilometers altit6ude. The temperature becomes very high, but the air has such a low density that it can hold very little heat. Any denser object in the thermosphere will be extremely hot in sunlight but very cold any night.

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