Mesosphere

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Earth atmosphere diagram showing the exosphere and other layers. The layers are to scale. From Earth's surface to the top of the stratosphere (50km) is just under 1% of Earth's radius.

This article is about the atmospheric mesosphere, for the Earth's mantle see Mesosphere (mantle).

The mesosphere (from the Greek words mesos = middle and sphaira = ball) is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. The mesosphere is located about 50 to 85 kilometers (30 to 50 miles) above the Earth's surface.^{[citation needed]}

The stratosphere and mesosphere are referred to as the middle atmosphere. The mesopause, at an altitude of 80-90 km, 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 weights.

Noctilucent clouds are located in the mesosphere. The Mesosphere is also the region of the Ionosphere known as the D Layer. The D Layer is only present during the day, when some ionization occurs with nitric oxide being ionized by Lyman series-alpha hydrogen radiation. The ionization is so weak that when night falls, and the source of ionization is removed, the free electron and ion form back into a neutral molecule.

[edit] Temperature

Within the mesosphere, temperature decreases with increasing altitude. This is due to decreasing solar heating and increasing cooling by CO₂ radiative emission. The top of the mesosphere, called the mesopause, is the coldest place on Earth. ^[1] Temperatures in the upper mesosphere fall as low as -100°C (-148°F or 173 K)^[2], varying according to latitude and season.

[edit] Dynamical Features

The main dynamical features in this region are atmospheric tides, internal atmospheric gravity waves (commonly called "gravity waves") and planetary waves. Most of these tides and waves are excited in the troposphere and lower stratosphere, and propagate upward to the mesosphere. In the mesosphere, gravity-wave amplitudes can become so large that the waves become unstable and dissipate. This dissipation deposits momentum into the mesosphere and largely drives its global circulation.

[edit] Mysterious Layer

The mesosphere lies above the maximum altitude for aircraft and below the minimum altitude for orbital spacecraft. It has only been accessed through the use of sounding rockets. As a result, it is the most poorly understood part of the atmosphere. This has caused scientists to refer disparagingly to the mesosphere and lower thermosphere as the ignorosphere.^[3]

[edit] Meteors

Millions of meteors burn up daily in the mesosphere as a result of collisions with the gas particles contained there; this creates enough heat to vaporize almost all of the falling objects long before they reach the ground, resulting in a high concentration of iron and other metal atoms there.

[edit] See also

• Edge of space
• Meteor
• Atmospheric reentry
• Atmospheric tide

[edit] References

[edit] External links

• Description with links to other atmospheric topics

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