FAA Ground School Practice Test

What happens to air stability when it is warmed from below?

1. It increases

2. It decreases

3. It remains unchanged

4. It becomes highly variable

The correct answer is: It decreases

When air is warmed from below, its stability decreases. This occurs because warmer air tends to rise, as it is less dense than the cooler air surrounding it. When the surface air is heated, it expands and becomes buoyant, leading to vertical motion. This vertical movement indicates a more unstable atmosphere because the rising warm air can lead to the development of convective currents, which may result in turbulence and the formation of clouds. In an unstable atmosphere, the lapse rate (the rate at which temperature decreases with an increase in altitude) is steeper than the dry adiabatic lapse rate, promoting the continuous rising of warm air. Consequently, as air warms from below, it encourages more mixing and vertical development, which correlates with reduced atmospheric stability.