Page 251 - PPL-engelsk 2025
P. 251
Meteorology
The polar front is an important climatic phenomenon because many weather
events such as low-pressure systems, storms, and rain are formed here, like
cyclones and low-pressure systems that can lead to severe weather, including
rain, snow, and strong winds.
The polar front typically occurs around 60° north latitude in the Northern
Hemisphere and around 60° south latitude in the Southern Hemisphere.
3.4.2.4 The Jet Stream
Due to the sharp transition in temperature and volume, isobaric surfaces at
higher altitudes form steep slopes that fall towards the poles. As a result, there
are large gradients at specific altitudes, generating very strong winds.
Since the Coriolis force is primarily dependent on wind speed, the deflection is
90°, and the wind becomes a geostrophic wind—i.e., wind that blows at higher
altitudes parallel to isobars (more on this later).
This wind is called the jet stream.
The jet stream is located 8–12 km above the Earth's surface. We can't feel it at
the surface, but it is very important for aviation and for moving low-pressure
systems (which you will hear about later).
3.4.2.5 The interdependence of high- and low-pressure systems
The illustration on the next page shows how high and low-pressure systems are
interrelated.
It starts at the top with normal pressure and temperature in both columns.
In the left column, high pressure builds up, while in the right column, low
pressure builds up.
Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 251
