What measurement can be used to determine the stability of the atmosphere?

The actual lapse rate is a crucial measurement for determining the stability of the atmosphere because it represents the rate at which air temperature decreases with an increase in altitude. In meteorology, understanding how the actual lapse rate compares to the standard lapse rate allows pilots and meteorologists to assess atmospheric stability.

When the actual lapse rate is greater than the standard lapse rate (which is approximately 3.5°F per 1,000 feet or 6.5°C per 1,000 meters), the atmosphere is considered unstable. In this scenario, rising air parcels can continue to ascend since they are warmer—and thus less dense—than the surrounding air. This can lead to the formation of convective currents and thunderstorms. Conversely, if the actual lapse rate is less than the standard lapse rate, the atmosphere is stable, and air parcels tend to resist upward movement.

While atmospheric pressure, surface temperature, and humidity can influence weather and flying conditions, they do not provide a direct measurement of atmospheric stability. Thus, relying on the actual lapse rate is essential for pilots in assessing conditions that may affect flight safety.