Page 277 - PPL-engelsk 2025

Meteorology

When the air rises, the pressure decreases, air molecules spread farther apart,

and the temperature drops. The expansion of the air causes a temperature drop

of 1°C per 100 meters of ascent (3°C per 1000 feet).

At a certain height, the dew point is reached, and clouds form.

This height is called the condensation level.

As the air continues to rise, condensation releases the latent heat that was used

for evaporation near the surface. This heat, which corresponds to 0.5°C per 100

meters of ascent (1.5°C per 1000 feet), must be subtracted from the cooling

caused by expansion.

Above the condensation level, the cooling rate is only 0.5°C per 100 meters of

ascent.

3.6.2 Clouds – Types

The type of clouds that form depends on the amount of moisture and the

stability of the air mass.

- Unstable air creates cumulus-shaped clouds, which have significant

vertical development.

- Stable air forms stratus clouds, which have a broad horizontal spread.

According to the international cloud classification, clouds are categorized in

two ways:
- By the altitude at which they are found.

- By their shape (which is determined by how they form).

Clouds are classified into main groups based on their appearance and

formation.

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 277