Plain English Meaning

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.

Full 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.

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 in its layer rather than churn up and down.