Definition
The boundary layer between the troposphere (the lower layer of the atmosphere where weather occurs) and the stratosphere (the layer above it). Its height varies from about 28,000 feet over the poles to about 56,000 feet over the equator, and it is characterized by a sudden change in temperature lapse rate.
Plain English
The dividing line in the sky between the lower part of the atmosphere, where almost all weather happens, and the calmer layer above it. Below this line, air gets colder as you climb. At and above it, that pattern stops.
Context Anchor
Seen in weather and high-altitude performance discussions, especially when temperature, winds, and turbulence near the top of the weather layer are being discussed.
Derivation
From the Greek tropos meaning 'turn' or 'change,' and the Latin pausa meaning 'a stop' or 'pause.' Literally, 'where the changing stops.' The name fits: below the tropopause, temperature keeps changing with altitude in a predictable way; at the tropopause, that change pauses.
Why Pilots Care
Turboprop performance calculations and altitude limits depend on knowing where temperature stops falling, which directly affects engine power and aircraft efficiency.
Grounding Statement
Imagine climbing through cooler and cooler air on the way up, then reaching a level where the temperature stops dropping. That level is the tropopause.
Intuition Check
The tropopause is not a solid ceiling or wall in the sky. It is a transition zone in the atmosphere where temperature behavior changes.
Example Sentence 1
Climbing through the tropopause, the crew noticed the outside air temperature stopped decreasing and the ride smoothed out.
Example Sentence 2
Pilots plan cruise altitudes below the tropopause to keep the denser air that turboprops need for best performance.