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Definition of TROPOSPHERE
: the lowest densest part of the earth's atmosphere in which most weather changes occur and temperature generally decreases rapidly with altitude and which extends from the earth's surface to the bottom of the stratosphere
Lowest region of the atmosphere, bounded by the Earth below and the stratosphere above, with the upper boundary being about 6–8 mi (10–13 km) above the Earth's surface. The troposphere is marked by decreasing temperature with height, which distinguishes it from the stratosphere. Most clouds and weather systems occur in the troposphere.