Page 309 - PPL-engelsk 2025
P. 309
Meteorology
3.8.5 Formation of low pressure
Low pressure forms when the air in an atmospheric region is heated and rises,
creating an area of lower pressure compared to the surroundings.
Low pressure occurs when warm air rises in the atmosphere. As the air rises, it
creates an area of lower pressure due to less air near the surface of the Earth.
This upward movement of air can happen due to solar heating, colliding air
masses, or convective heating.
As the air rises, it cools and condenses, forming clouds and possibly leading to
precipitation. At the same time, air from the surroundings flows into the low-
pressure area to replace the stagnant air, which creates cyclonic rotation
(counterclockwise) in the low-pressure system.
The first step in the formation of a front is due to flow phenomena in the frontal
zone (where warm and cold air meet). Where the flow (wind) is strongest, the
pressure is lowest. The winds are deflected by the Coriolis effect, resulting in
winds that rotate counterclockwise around low-pressure systems.
3.8.5.1 Dynamic Low Pressure
The low-pressure systems in the global system, which you have read about
earlier, form when air is heated and rises, and because this happens
continuously (due to the sun) and at roughly the same locations, they are
considered stationary.
On the polar front (the boundary between polar air and tropical air), dynamic
fronts are formed, which often pass through Denmark. These are called
mowing or dynamic low pressures.
Dynamic low pressures result from disturbances in the upper layers of the
atmosphere around the polar front. They do not form in specific places and are
thus called dynamic low pressures.
Dynamic low pressures are typical weather conditions in Denmark.
Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 309
