The mesosphere (/ˈmɛsoʊsfɪər/; from Greek mesos "middle" ) is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. In the mesosphere, temperature decreases as the altitude increases. This characteristic is used to define its limits: it begins at the top of the stratosphere (sometimes called the stratopause), and ends at the mesopause, which is the coldest part of Earth's atmosphere with temperatures below −143 °C (−225 °F; 130 K). The exact upper and lower boundaries of the mesosphere vary with latitude and with season (higher in winter and at the tropics, lower in summer and at the poles), but the lower boundary is usually located at heights from 50 to 65 kilometres (164,000 to 213,000 ft; 31 to 40 mi) above the Earth's surface and the upper boundary (mesopause) is usually around 85 to 100 kilometres (53 to 62 mi).
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