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Meteorology

If an air mass is warmer than its surroundings, it will rise.

If an air mass is colder than its surroundings, it will sink towards the ground.

3.3.3.1 Dry adiabat and saturated adiabat

In the illustration above, the air mass on the left is an almost dry air mass, with
o
a temperature of 20 C and a relative humidity of 30%.

o
The first part of the ascent - up to 2 km - occurs with a temperature drop of 1 C
per 100 m (called the dry adiabat).

In 2 km, the relative humidity is 100%, and the invisible water vapor becomes

a visible cloud, which is formed by condensation. Then the ascent occurs when

the air humidity has reached 100%, and clouds are formed with a temperature

o
drop of 0.5 C per 100 m (called the saturated adiabat).

After that, the temperature drops up to 3 km with a temperature drop of 5

degrees per km. This is the saturated adiabatic temperature drop with height.

The reason why the temperature now only drops by 5 degrees per km is that

heat is released during condensation.

3.3.3.2 Stable and unstable air mass

Note that the air mass on the left is always colder than the surrounding air, and

it must be forced up. The air mass is said to be stable.

The air mass on the right is a very humid air mass, and when it is moved 1 km

up, its temperature will be 15 degrees, and it will be 100% saturated with

moisture. The surrounding air is 14 degrees. The 15 degrees warm air will now

tend to rise by itself! The air mass is said to be unstable.

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Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 224