Definition
The layer of Earth's atmosphere directly above the troposphere, extending from roughly 36,000 feet (the tropopause) up to about 160,000 feet. In this layer, temperature is essentially constant or increases with altitude, and the air is very stable, dry, and largely free of weather.
Plain English
The calm, stable layer of air that sits above the weather layer. It starts around 36,000 feet up and extends much higher, with smooth air and almost no clouds or storms.
Context Anchor
Seen in weather, atmospheric, engine performance, and high-altitude flight discussions when describing the layers of air above Earth.
Derivation
From Latin stratum, meaning 'layer' or 'something spread out,' combined with sphere. The name reflects the fact that this part of the atmosphere is layered and stratified, with little vertical mixing — air tends to stay in its layer rather than churn up and down.
Why Pilots Care
Jet aircraft cruise here for fuel efficiency, smooth air, and reduced drag.
Grounding Statement
Picture the atmosphere as stacked layers. The bottom layer (troposphere) is where weather happens and where the air gets colder as you climb. Step up into the stratosphere and the cooling stops — the air becomes smooth, thin, and steady.
Intuition Check
Do not think of the stratosphere as outer space. It is still part of Earth’s atmosphere; it is simply a higher layer above most weather.
Example Sentence 1
Cruising in the lower stratosphere, the flight crew enjoyed smooth air and clear skies above the weather.
Example Sentence 2
At cruise altitude in the stratosphere the aircraft experienced smooth air and better fuel economy.