CAAP Private Pilot License (PPL) Meteorology Practice Test 2026 - Free PPL Meteorology Practice Questions and Study Guide

Stability depends on how fast the surrounding air cools with height compared to how fast a dry air parcel cools as it rises. The dry adiabatic lapse rate is about 9.8°C per kilometer (roughly 5.5°F per 1000 ft). If the environmental lapse rate matches that same rate, the displaced parcel cools at the same rate as its surroundings, so it remains at the same density as the surrounding air. There’s no buoyant force to push it back or to lift it further, so the air is neutrally buoyant and neutrally stable.

If the environmental lapse rate were steeper than the dry adiabatic rate, the environment would cool more quickly with height than the parcel does, making the parcel relatively warmer and less dense as it rises, so it would tend to continue rising (unstable). If the environmental lapse rate were gentler than the dry adiabatic rate, the parcel would become cooler and denser than its surroundings as it rises, so it would sink back down (absolutely stable).