mesosphere

Etymology

meso- + -sphere

noun

1. (meteorology) The layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere.
   The mesosphere may be described as the earth's intermediate or middle atmosphere, which separates the thermosphere above from the ozonosphere (or stratosphere) below, both of which are responsible for absorption of most of the ultraviolet part of the solar radiation and preventing it from reaching the earth's surface. 2008, Kshudiram Saha, The Earth's Atmosphere: Its Physics and Dynamics, Springer Science & Business Media, page 102
2. (geology) The part of the Earth's mantle below the asthenosphere and above the outer core.