Definition
The layer of Earth's atmosphere directly above the troposphere, beginning at roughly 36,000 feet (varying by latitude) and extending to about 160,000 feet. It is characterized by stable air, very little water vapor, no significant weather, and a temperature that initially remains constant with altitude before increasing higher up.
Plain English
The calm, dry layer of the atmosphere that sits above the layer where weather happens. It begins around 36,000 feet and contains almost no clouds, turbulence, or storms.
Context Anchor
Seen in aviation weather discussions, especially when learning the layers of the atmosphere and where most weather occurs.
Derivation
From Latin 'stratum' meaning 'layer' and Greek 'sphaira' meaning 'sphere' or 'ball.' Literally 'the layered sphere' — named because the air settles into stable horizontal layers without the vertical mixing seen in the troposphere below.
Why Pilots Care
Flight in the lower stratosphere is generally smooth and free of weather, which is why high-altitude jet operations cruise near or just below it. Knowing where the stratosphere begins also helps pilots understand the tropopause, jet streams, and clear-air turbulence found at that boundary.
Analogy
Think of the atmosphere like a stack of clear blankets around Earth. The stratosphere is the blanket above the lowest one, where most weather is found.
Grounding Statement
Above this boundary the air becomes calm, thin, and dry — weather essentially stops.
Intuition Check
Do not read this as “stratos-here.” The intended aviation term is stratosphere, the atmospheric layer above the lower weather layer.
Example Sentence 1
Most thunderstorms top out at the tropopause because rising air cannot easily push into the stable stratosphere above it.
Example Sentence 2
Above the troposphere the stratoshere offers stable conditions for long-range cruise flight.