Page 259 - PPL-engelsk 2025

Meteorology

However, if you come from the leeward side, you may encounter severe

turbulence in the form of rotor winds. One moment, you are climbing at 1000

feet per minute, and the next moment, you’re descending at 2000 feet per

minute.

This is obviously a dangerous situation.

If wave clouds, the lens-shaped Alto Cumulus Lenticularis, are present, this

indicates conditions where rotors might be hidden on the leeward side. Thus,

mountains should be flown over at a safe altitude.

3.4.4.5 Valley winds and mountain winds

The figure shows the formation of valley and mountain winds. During the day,

the air heats up in the valley and rises along the mountain slopes.

Updrafts are called anabatic winds.

Updrafts are not as strong due to

gravity's effect.

At night, the air cools and sinks from
the mountain, creating a mountain

wind (named by where it originates).

Downdrafts are called katabatic

winds.

Katabatic winds are stronger than anabatic winds due to the gravity's effect on

the cold, heavy air that moves downward.

How to remember the difference between ana-batic and kata-batic?

Think, during the day ANA goes up the mountain. It would be a "KATAstrophe"

if she fell down.

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Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 259