1. Wet equatorial climate (Af. Am) -
Bringing together the information on global pattern of weather elements it will be seen that within 50 of latitude north and south of the equator the following conditions prevail:
(a) Temperatures average close to 80°F(27°C) for every month, so that the annual range is extremely small.
(b) Air pressures average between 1009 and 1012 mb, or slightly less than normal sea-level pressure.
(c) The general flow of air is from east to west in the tropical easterlies at high altitude, but somewhat more equatorward in the surface trade winds, which originate in the subtropical high-pressure cells. Here, then, is a region of converging warm, unstable air masses meeting along the equatorial trough.
(d) Examination of the world rainfall map shows this to be a belt of heavy rainfall, exceeding 80 in (200 cm) annually for the most part.
From the above information we can compile a description of the wet equatorial climate. Average annual temperatures are close to the 80°F(27°C) mark; seasonal range of temperature is so slight as to be imperceptible because the sun is high throughout the year. Rainfall is heavy during the entire year, but with considerable differences in monthly averages because of the seasonal shifting of the equatorial convergence zone and a consequent variation in air mass characteristics.
According to Koppen's definition of this Af climate, no month averages less than 2.4 in (6 cm) of rainfall.
An especially noteworthy feature is that the daily range is normally from 15 to 20°F (8 to 11°C), a vastly greater range than the annual range of monthly mean temperatures. In other words, daily variations far exceed seasonal variation in the wet equatorial climate.
The fact that some stations show one maximum and one minimum in the rainfall graph, whereas others have two maxima and two minima is not easily explained, but is probably attributable to a rather complex series of seasonal changes in air mass movements and positions of the equatorial trough.
The soil-moisture regime is of the equatorial type in which large water surpluses are generated in most months of the year.
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