TROPICAL AIR CIRCULATION A REVIEW OF THE RECENT LITERATURE*
Authors: KERR DONALD 
Published: March 2008

ABSTRACT. . Since World War 11 research programmes on tropical meteorology have been greatly enlarged and much new literature on the winds and weather of the Tropics has appeared. Accord has been reached on the underlying physical bases of most circulation patterns, but sharp disagreement persists on some aspects, in particular those referring to tropical fronts. This paper attempts, within the framework of the classical circulation systems, the trades, doldrums and monsoons, to review the recent literature and to abstract what is most significant for the geographer.

RÉSUMÉ. . Depuis le dernier conflit mondial, la recherche dans le domaine de la météorologie tropicale a connu un essor prestigieux et nombre d'ouvrages sur ce sujet furent publicés. Depuis lors, un accord est intervenu en ce qui concerne les causes physiques des principaux systèmes de circulation atmosphérique, mais quelques différences persistent toujours sur certains points, surtout ceux se rapportant à l'étude des fronts tropicaux. Cette étude pour sa part, examine les ouvrages récents traitant des systèmes conventionnels de circulation, tels que les alizés, les doldrums, et les moussons, et tente d'y en retirer ce qui est le plus significatif pour le géographe.

To sum up, the following comments are offered.

Upper air circulation in the Tropics can no longer be ignored in any study of the dynamic climatology of low latitudes.

The trade winds undergo considerable modification as they blow over the warm oceans. In the eastern oceans they are relatively dry and stable (aloft), and here they attain the highest degree of constancy of direction. To the west they become increasingly disturbed by easterly waves, and rainfall increases accordingly. Where the trajectory over the ocean is short (South Atlantic Ocean) such modification is normally not accomplished; where it is long (over the Pacific Ocean) great modifications take place.

There is no constant convergence of the trades at or near the equator, and the clash of the trades depicted on models of the general circulation is, for the most part, imaginary. Really significant convergence occurs only in organized disturbances. Many of the trade wind currents never reach the equator, having veered poleward around the western branches of the sub‐tropical oceanic highs. On the other hand, trade wind currents will, from time to time, cross the equator and deeply penetrate the opposite hemisphere. It hears repetition that the trades blow in surges, their trajectories being determined by the particular orientation of pressure systems.

Most of the rain in the low latitudes comes from organized disturbances and not from isolated “heat” thunder showers. Land elevations, however, influence the distribution of rain very greatly and, for example, the windward slopes of oceanic islands receive much more rain than their leeward counterparts. The frequency and intensity of both equatorial weather disturbances and trade wind weather disturbances varies greatly from one region to another, and from one year to another. More studies are urgently needed, however, to define more precisely rainfall variability in the Tropics which appear to be higher than at once thought.