Stability is defined by which concept in atmospheric science as described in the material?

• A. Stability is defined by the environmental lapse rate comparison to adiabatic rates, with stable air resisting vertical motion.
• B. Stability is determined by humidity alone.
• C. Stability is determined by surface wind speed only.
• D. Stability is determined by air pressure alone.

Answer: (A)

Stability is about how the air temperature changes with height and how a parcel of air would behave if it were lifted. The environmental lapse rate tells you how quickly the surrounding air cools with height. A parcel that rises cools or warms at a specific adiabatic rate (dry adiabatic lapse rate is about 9.8°C per km, with the moist rate being lower when moisture is involved). If the surrounding air cools more slowly with height than the parcel does, the lifted parcel becomes cooler than its surroundings and more dense, so it tends to sink back down. That means the atmosphere resists vertical motion and is stable. If the environment cools faster with height than the parcel, the parcel stays warmer and buoyant, so it continues to rise and the atmosphere is unstable. Thus, stability is defined by comparing the environmental lapse rate to these adiabatic rates.