mesosphere,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 but occasionally the
mesopeak. 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.  The
amount percentage of oxygen, nitrogen, and carbon dioxide in the
air in the mesosphere is essentially the same as that in the
levels of the Earth’s atmosphere immediately above the Earth’s
surface. The principal differences are that the density of the
air is much less, there is apparently very little water vapour
in the mesosphere, and the mesosphere contains higher
percentages of ozone than the lower levels.