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The region of the atmosphere from 30 to 190 kilometers (20 to 120 miles) above the earth's surface, in which photochemical reactions initiated by solar radiation occur.
(Physical Geography) meteorol a rare name for thermosphere
che•mo•sphere(ˈki məˌsfɪər, ˈkɛm ə-)
the region of the atmosphere most characterized by chemical, esp. photochemical, activity, starting in the stratosphere and including the mesosphere and perhaps part of the thermosphere.