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Meteorology
3.5.4 Stable and unstable air
We discuss three forms of stability regarding air:
- Stable air mass
- Unstable air mass
- Conditionally unstable air mass
3.5.4.1 Stable, unstable and conditionally unstable air masses
When a parcel of air is colder than its surroundings, its density will be greater,
and it will sink.
When the air layer is stable, the temperature drop in the atmospheric air will
be less than 1.5°C per 1,000 feet (saturated adiabatic gradient).
When a parcel of air is warmer than its surroundings, for example, after air mass
movement, its density will be less, and it will rise.
When the air layer is unstable, the temperature drop in the atmospheric air will
be more than 3°C per 1,000 feet (dry adiabatic gradient).
When a parcel of air is stable under certain conditions and unstable under
others, this is called conditional instability.
The diagram below shows the relationship between the three forms of stability.
Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 271
