Today we will talk about air stability and most importantly - how and why to distinguish stable and unstable atmospheric stratification.
Everything depends on air temperature. Let’s recall that warm air is less dense and lighter than cold air, so it tends to rise up from the warmed ground, and cold air from higher layers - to go down.
If the atmosphere slowly cools down with height (less than 1°C with every 100 meters), the air is stable - it’s stable stratification. In this case, the rising or descending air slows down after reaching the same temperature as the surrounding air. Stable air is generally slow-moving.
But if the atmosphere cools down faster than 1°C with every 100 meters of height, the air no longer has enough time to cool down and does not slow down but accelerates with vertical movement. Then the air is unstable - it’s unstable stratification.
In an unstable atmosphere, the air moves quickly up and down - all air passengers are familiar with turbulence. In humid climates instability leads to thundercloud formation, which above warm oceans can become a tropical cyclone. In dry climates, it can cause mirages, dust and water vortices (tornados).
In stable air, there is no turbulence, but there are fogs, drizzles, and smog from air pollution in cities.
Although instability is associated with a large number of different incidents, warm upward flows in such air provide good conditions for soaring - particularly for paragliding. Stable air is more suitable for powered paragliding.
Signs of stability:
• the sky is covered by solid clouds or the cloudiness is variable;
• layered clouds;
• smoke rises to a certain level and spreads there;
• steady wind;
• poor visibility.
Signs of instability:
• a clear, cloudless night followed by a clear morning;
• heaped clouds;
• very high rising smoke;
• gusty wind;
• good visibility.