If the temperature remains constant or increases with altitude, how is the air classified?

When the temperature remains constant or increases with altitude, the air is classified as stable. In stable air, vertical movement is limited because the air above is warmer than the air below; warmer air is less dense than cooler air, leading to a situation where the cooler, denser air is effectively trapped beneath. This suppresses convection and can prevent the development of significant turbulence or vertical motion, which is typical in unstable air.

In contrast, unstable air occurs when the temperature decreases with altitude, allowing warm surface air to rise freely. Mixed air refers to conditions where both stable and unstable layers may be present, while variable air does not have a strictly defined temperature profile or stability condition. Recognizing the stability of air is vital for pilots, as it influences weather patterns, turbulence levels, and overall flight safety.