Atmospheric Stability

Atmospheric stability describes the tendency of a parcel of air to continue moving vertically or return towards its original level after being disturbed.

Stable Air

A parcel of stable air, when disturbed vertically, tends to return towards its original level.

Stable air is commonly associated with:

• stratiform or flat cloud;
• smooth flying conditions;
• poor vertical mixing; and
• haze or smoke trapped near the surface.

Remember:

Stable = Stratus and Smooth

Unstable Air

A parcel of unstable air, when displaced vertically, tends to continue moving farther away from its original level.

Unstable air is commonly associated with:

• cumuliform or lumpy cloud;
• strong vertical air movement;
• turbulence; and
• showers or thunderstorms if sufficient moisture is present.

Remember:

Unstable = Cumulus and Bumpy

Conditionally Unstable Air

Conditionally unstable air behaves differently depending on whether it is dry or saturated.

It may be:

• stable while unsaturated; but
• become unstable after saturation and cloud formation.

This occurs because saturated air cools more slowly as it rises than dry air.

Temperature and Stability

The stability of a rising or sinking parcel of air depends on its temperature compared with the surrounding air.