8.4 Weather Maps

8.4.2 Identify the following features found on surface weather maps:

8.4.4 Explain the most common weather characteristics of each feature.

(a) isobars;

Isobars are lines on a weather map joining places of equal atmospheric pressure.

The spacing of isobars indicates the strength of the pressure gradient.

• Close isobars indicate a strong pressure gradient and usually stronger winds.
• Widely spaced isobars indicate a weak pressure gradient and usually lighter winds.

(b) anticyclone (“high”);

In the Southern Hemisphere, an anticyclone is an anticlockwise circulation of air around a central area of high pressure.

A high-pressure system:

• Has higher pressure at its centre than the surrounding area.
• Usually has sinking air.
• Has winds that tend to flow outward from the high-pressure area.
• Is usually marked on a weather map with an H.

Common weather characteristics include:

• Fine weather
• Settled conditions
• Light winds
• Less cloud
• Stable air
• Possible fog or poor visibility if moisture is present

(c) depression (“low” or “cyclone”);

In the Southern Hemisphere, a depression is a clockwise circulation of air around a central area of low pressure.