Environmental Engineering Reference
In-Depth Information
EQUATORIAL TROUGH
The traditional idea of the equatorial climate involves the daytime build-up of
convectional clouds into massive cumulonimbus displays. Rainfall is frequent and
abundant, temperatures and humidity are high, acting together to give us the tropical rain
forests. At night the air is humid and still. Condensation takes place on to the forest trees,
and the sound of moisture dripping to the forest floor competes with that of the wildlife.
The structure of the atmosphere, though, is not as simple as this model may suggest.
The multitude of names
Figure 28.1
The humid tropics in
relation to the main trade-wind zones.
Areas towards the boundary of the
region are humid for part of the year
only.
which have been used for the area give some idea of its variety - the Doldrums, the
intertropical front, the intertropical convergence zone, intertropical trough, equatorial
trough or intertropical confluence zone. For simplicity we shall refer to it as the
equatorial trough, although it does extend towards the subtropics, and is quite variable in
character.
The equatorial trough has many different forms. It represents the area of low pressure
somewhere near the equator towards which the trade winds blow. The precise form it
takes will depend upon the stability of the trades, their moisture content and the degree of
convergence and uplift. Much of the trough is over the oceans and it is only recently that
satellite photographs have shown us more about the detail of cloud forms (Plate 7.1) and
the pattern of its movements (Figure 28.2).
The structure of the trough is variable, with an element of a hierarchy of cloud. Larger
elements called cloud clusters, perhaps 100 km to 1000 km in length, may be found.
Within the cluster there are convective cells, and embedded in the cells are individual
convective elements which can give the heavy rain characteristic of the equatorial trough.
