Page 288 - PPL-engelsk 2025

Meteorology

B. The cooling of the lower layers of air occurs, and a low inversion forms.

C. As the cooling process progresses, the temperature drops, and the

inversion layer becomes thicker.

For the formation of radiation fog, it is a condition that the sky is clear, some

moisture must be present in the air.

This type of fog is common in low-lying areas such as valleys or flat landscapes.

3.6.6.2 Advection fog

Advection is the horizontal movement of an air mass.

Advection fog forms when warm, moist air moves over a cooler surface (e.g.,

the sea or snow). When the air temperature drops to the dew point, water

vapor condenses and forms fog.

The wind will typically be 15-25 knots.

Imagine the advection
of warm, moist air over

cold land.

As shown in the diagram

here, warm, moist air
blows over land.

The air cools to the dew point temperature, and the type of fog known as
advection fog forms.

The more the air cools, the denser the fog becomes.

Advection fog is the type of fog with the greatest spread – both horizontally

and vertically.

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 288