Mesosphere

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This article is about the atmospheric mesosphere, for the Earth' 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 50-80/85km above Earth's surface. Within this layer, temperature decreases with increasing altitude. The main dynamical features in this region are the atmospheric tides which are driven by momentum propagating upwards from the lower atmosphere and extending into the lower thermosphere.

Atmosphere diagram showing the mesosphere and other layers. The layers are not to scale: from Earth's surface to the top of the stratosphere (50km) is just under 1% of Earth's radius.

Because it lies between the maximum altitude for most aircraft and the minimum altitude for most spacecraft, for a long time this region of the atmosphere has only been accessed through the use of sounding rockets. As a result the region is one of the most poorly understood in the atmosphere. This has led the mesosphere and the lower thermosphere to be jokingly referred to by scientists as the ignorosphere [1] [2].

Temperatures in the upper mesosphere fall as low as -100°C (-146°F or 173 K) [3], varying according to latitude and season. Millions of meteors burn up daily in the mesosphere as a result of collisions with the gas particles contained there, leading to a high concentration of iron and other metal atoms. The collisions almost always create enough heat to burn the falling objects long before they reach the ground.

The stratosphere and mesosphere are referred to as the middle atmosphere. The mesopause, at an altitude of about 80 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 scale heights of different chemical species will differ. Noctilucent clouds are located in the mesosphere.