[mez-uh-sfeer, mes-, mee-zuh-, -suh-]
(in the classification of the earth's atmosphere by chemical properties) the region between the ionosphere and the exosphere, extending from about 250–650 miles (400–1050 km) above the surface of the earth.
(in the classification of the earth's atmosphere by thermal properties) the region between the stratosphere and the thermosphere, extending from about 20–50 miles (32–80 km) above the surface of the earth.

1945–50; meso- + -sphere

mesospheric [mez-uh-sfer-ik, mes-, mee-zuh-, -suh-] , adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
mesosphere (ˈmɛsəʊˌsfɪə)
1.  the atmospheric layer lying between the stratosphere and the thermosphere, characterized by a rapid decrease in temperature with height
2.  the solid part of the earth's mantle lying between the asthenosphere and the core

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
mesosphere  [%PREMIUM_LINK%]     (měz'ə-sfîr')  Pronunciation Key 
The region of the Earth's atmosphere lying above the stratosphere and below the thermosphere, from a height of about 50 km (31 mi) to about 80 km (50 mi) above the Earth's surface. In the mesosphere temperatures decrease with increasing altitude due to the decreasing absorption of ultraviolet radiation from the Sun. At the top of this region temperatures are around -95°C (-135.4°F). Most of the meteors that enter Earth's atmosphere burn up while passing through the mesosphere. See also exosphere, stratosphere, thermosphere, troposphere., See illustration at atmosphere.

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Encyclopedia Britannica


region of the upper atmosphere between about 50 and 80 km (30 and 50 miles) above the surface of the Earth. The base of the mesosphere is defined as the temperature maximum existing at the top of the stratosphere, with the boundary between the two regions usually called the stratopause. The mesosphere extends upward to the next temperature minimum, which defines the base of the thermosphere; the boundary between the two regions is called the mesopause.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
Many telescopes with adaptive optics already use lasers to make sodium atoms in the mesosphere fluoresce.
Not only has the stratosphere in the ozone layer cooled, but so has the mesosphere above the ozone layer.
The transition boundary which separates the stratosphere from the mesosphere is called the stratopause.
Above that is the mesosphere, where the lowest temperatures anywhere in the atmosphere occur.
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