Page 230 - PPL-engelsk 2025

Meteorology

At the top of the diagram (in the red oval), you can see what the pressure

system looks like from A to B when viewed from the front.

The isobars are the circles drawn around high and low-pressure areas. Each

circle (isobar) indicates a specific pressure.

For clarity, numbers are shown on the cross-section (the red oval), which also

illustrates the difference in pressure between high and low-pressure areas.

For example, the high-pressure area in the center on the left, where the

pressure is highest, has a pressure of 1030 hPa. The pressure decreases away

from the center of the high-pressure area.

In this diagram, the isobar spacing is 5 hPa. On the weather maps we will work

with later, the isobar spacing is 4 hPa.

3.3.5.5 Ridges and troughs

Often, a U- or V-shaped area extends from a low-pressure or high-pressure

area.

This protrusion is called a

trough in low-pressure

areas and a ridge in high-

pressure areas.

When flying at what seems like a constant altitude, what you're actually

following is constant pressure, e.g., 1000 hPa.

3.3.5.6 Air can be compressed

Air has the property of being compressible (able to be pressed together).

The higher the pressure, the smaller the volume of air.

At sea level, the air is most compressed, and the higher you go, the more the

air expands.

If you heat a volume of air, it will expand.

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 230