What is "mesosphere"

1950, from meso- + second element in atmosphere.

n. layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere

n. the atmospheric layer between the stratosphere and the thermosphere

The mesosphere (; from Greek mesos "middle" and sphaira "ball") is the layer of the Earth's atmosphere that is directly above the stratopause and directly below the mesopause. In the mesosphere, temperature decreases as the altitude increases. The upper boundary of the mesosphere is the mesopause, which can be the coldest naturally occurring place on Earth with temperatures below . The exact upper and lower boundaries of the mesosphere vary with latitude and with season, but the lower boundary of the mesosphere is usually located at heights of about above the Earth's surface and the mesopause is usually at heights near , except at middle and high latitudes in summer where it descends to heights of about .

The stratosphere, mesosphere and lowest part of the thermosphere are collectively referred to as the "middle atmosphere", which spans heights from approximately to . The mesopause, at an altitude of , separates the mesosphere from the thermosphere—the second-outermost layer of the Earth's atmosphere. This is also around the same altitude as the turbopause, below which different chemical species are well mixed due to turbulent eddies. Above this level the atmosphere becomes non-uniform; the scale heights of different chemical species differ by their molecular masses.

In geology, the mesosphere refers to the mantle in the region under the lithosphere and the asthenosphere, but above the outer core. The upper boundary is defined as the sharp increase in seismic wave velocities and density at a depth of . At a depth of 660 km, ringwoodite (gamma-(Mg,Fe)SiO) decomposes into Mg-Si perovskite and magnesiowustite. This reaction marks the boundary between upper mantle and lower mantle. This measurement is estimated from seismic data and high-pressure laboratory experiments.

The base of the mesosphere includes the D' zone which lies just above the mantle-core boundary at approximately . The base of the lower mantle is at about 2700 km.

"Mesosphere" (not to be confused with mesosphere, a layer of the atmosphere) is derived from “mesospheric shell”, coined by Reginald Aldworth Daly, a Harvard University geology professor. In the pre- plate tectonics era, Daly (1940) inferred that the outer earth consisted of three spherical layers: lithosphere (including the crust), asthenosphere, and mesospheric shell. Daly’s hypothetical depths to the lithosphere–asthenosphere boundary ranged from , and the top of the mesospheric shell (base of the asthenosphere) were from . Thus, Daly’s asthenosphere was inferred to be thick. According to Daly, the base of the solid Earth mesosphere could extend to the base of the mantle (and, thus, to the top of the core).

A derivative term, mesoplates, was introduced as a heuristic, based on a combination of "mesosphere" and "plate", for postulated reference frames in which mantle hotspots apparently exist.

Mesosphere usually refers to:

• Mesosphere - the region of the Earth's atmosphere directly above the stratopause
• Mesosphere (mantle) - the region of the Earth's mantle (geology) just above the outer core
• The Mesosphere data center operating system based on Apache Mesos, and a company by the same name