CPL » Meteorology » Atmospheric Stability
20.18 Atmospheric Stability
20.18.2 Explain how atmospheric stability is determined.
Atmospheric stability is determined by comparing the temperature of a vertically displaced parcel of air with the temperature of the surrounding atmosphere at the same altitude.
When a parcel of air rises, it expands and cools due to the reduction in atmospheric pressure. Whether it continues to rise or returns to its original level depends on its temperature and density relative to the surrounding air.
Stable air
- A rising parcel becomes colder and denser than the surrounding air.
- It tends to sink back towards its original level when the lifting force is removed.
- Stable air therefore resists vertical movement.
Unstable air
- A rising parcel remains warmer and less dense than the surrounding air.
- It tends to continue rising without further external lifting.
- Unstable air therefore encourages vertical movement.
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