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STRUCTURE OF ATMOSPHERE: The Atmosphere is divided into layers according to major changes in temperature. Gravity pushes the layers of air down on the earth's surface.

The 4 layers are: 1.TROPOSPHERE 2.STRATOSPHERE 3.MESOPHERE 4.THERMOSPHERE

1.TROPOSPHERE -(0-12KM) The troposphere is the atmospheric layer closest to the planet and contains the largest percentage (around 80%) of the mass of the total atmosphere. Temperature and water vapor content in the troposphere decrease rapidly with altitude. Water vapor plays a major role in regulating air temperature because it absorbs solar energy and thermal radiation from the planet's surface. The troposphere contains 99 % of the water vapor in the atmosphere. Water vapor concentrations vary with latitude. They are greatest above the tropics, where they may be as high as 3 %, and decrease toward the polar regions.

2.STRATOSPHERE-(12-50KM) The stratosphere is the second major strata of air in the atmosphere. It extends above the tropopause to an altitude of about 30 miles (50 km) above the planet's surface. The air temperature in the stratosphere remains relatively constant up to an altitude of 15 miles (25 km). Then it increases gradually to up to the "stratopause".

3.MESOSPHERE -(50-80KM) This is the lower part of the stratosphere.The mesosphere a layer extending from approximately 30 to 50 miles (50 to 85 km) above the surface, is characterized by decreasing temperatures.

4.THERMOSPHERE-(80KM and UP) The thermosphere is located above the mesosphere. The temperature in the thermosphere generally increases with altitude reaching 600 to 3000 F (600-2000 K) depending on solar activity.

This layer contains: i)Ionosphere ii)Exosphere