Troposphere 

The troposphere is the lowermost portion of Earth's atmosphere and the one in which most weather phenomena occur; this layer extends to an altitude of 7-17 km, depending on latitude. Generally, jets fly near the top of this layer. The troposphere is directly below the stratosphere.

The word troposphere stems from the Greek "tropos" for "turning" or "mixing". This region, constantly in motion, is the densest layer. Nitrogen and oxygen are the primary gases, within this region.

The tropopause marks the limit of the troposphere and the beginning of the stratosphere. The temperature above the tropopause increases slowly with height up to about 50 km.

In telecommunication, the term troposphere has the following meanings:

1. The lower layers of atmosphere, in which the change of temperature with height is relatively large. It is the region where clouds form, convection is active, and mixing is continuous and more or less complete.

2. The layer of the Earth's atmosphere, between the surface and the stratosphere, in which temperature decreases with altitude and which contains approximately 80% of the total air mass.

Note: The thickness of the troposphere varies with season and latitude. It is usually 16 km to 18 km thick over tropical regions, and less than 10 km thick over the poles.

Source: from Federal Standard 1037C and from MIL-STD-188 and from the Department of Defense Dictionary of Military and Associated Terms

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