FAA Ground School Practice Test

What condition would decrease the stability of an air mass?

1. Cooling from above

2. Warming from below

3. Increasing wind speeds

4. Lowering humidity levels

The correct answer is: Warming from below

Warming from below decreases the stability of an air mass because it causes the lower layers of the atmosphere to become less dense and more buoyant. When the surface of the Earth warms, the air directly above it also warms, rising due to its lower density. As this warm air ascends, it can lead to the development of turbulence and convection processes that create unstable conditions. This is a fundamental principle in meteorology: stable air tends to resist vertical motion, while warmer air below creates an environment conducive to rising air, leading to instability. Cooling from above, increasing wind speeds, and lowering humidity levels typically contribute to or maintain stability in an air mass. Cooling from above creates a temperature inversion, which stabilizes the air by keeping warmer air above cooler air. Increasing wind speeds can help mix the air but often doesn't promote instability on its own. Lowering humidity levels generally results in denser air, which can also contribute to stability. Each of these scenarios supports the maintenance of stable air conditions, in contrast to the effects of warming from below.