Environmental Engineering Reference
In-Depth Information
uniform distributions of temperature and humidity over large areas - for example, Siberia
in winter. Whether or not the air will fully reach equilibrium with the surface
characteristics will depend upon how long it remains over the source region.
The character of an air mass is dependent upon conditions in the area in which it
forms. Because of this it is possible to classify air masses on the basis of their source
Plate 7.1 Meteosat image taken at 12.00 GMT on 17 March
2001 in the infra-red waveband. The cloud-free area of the
Saharan subtropical anticyclone is evident, with an
interesting rope-like cloud over the western Sahel. In the
southern hemisphere we can see the cloud spirals of mid-
latitude cyclones with a cloud band extending from the south
Atlantic to Brazil. Near the equator, especially over West
Africa, greater cloud development can be seen at the
equatorial trough. Comparison with Plate 3.1, which is in the
visible waveband, determines cloud-top heights. High clouds
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