Definition
The third layer of Earth's atmosphere, located above the stratosphere and below the thermosphere, extending roughly from 50 km (about 31 miles) to 85 km (about 53 miles) above the surface. Temperature decreases with altitude through this layer, reaching the coldest point in the atmosphere near its upper boundary.
Plain English
A high atmospheric layer well above where airplanes fly. It sits above the stratosphere and is the coldest part of the atmosphere.
Context Anchor
Seen in atmospheric-layer discussions in the Instrument Flying Handbook, especially when placing aviation weather and instrument flying in the lower part of the atmosphere.
Derivation
From Greek 'mesos' meaning 'middle,' plus 'sphere.' It is the middle layer in the standard atmospheric stack of troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
Why Pilots Care
Pilots do not fly in the mesosphere, but knowing where it sits helps build a clear mental map of the atmosphere and shows how high the layers pilots actually use (the troposphere and lower stratosphere) really are in comparison.
Grounding Statement
Picture five stacked layers of atmosphere from the ground up; the mesosphere is the third one, far above any aircraft, where shooting stars burn up.
Intuition Check
Do not read “mesosphere” as a layer where normal airplanes operate. For pilots, it is mostly a reference layer that helps organize the atmosphere above the weather and flight environment.
Example Sentence 1
The handbook lists the mesosphere as the layer above the stratosphere when describing the structure of the atmosphere.
Example Sentence 2
Most meteors disintegrate in the mesosphere before reaching lower levels of the atmosphere.