THE GENERAL CIRCULATION OF THE TROPICAL AND EQUATORIAL ATMOSPHERE

Abstract

Recent experiences with tropical meteorology around the world have brought to light the frequent existence of a zonal band of west winds in the vicinity of the equator, which appears not to be associated with the westerlies of middle latitudes, but which rather seems to be found between the trades of the two hemispheres. The boundaries of the equatorial westerlies are usually characterized by increased cloudiness and poor weather. In this paper an attempt is made to prove that the westerlies of equatorial regions are not simply transitory phenomena but instead should be considered as an integral part of the normal general circulation of the atmosphere. Seasonal variation of the latitude of maximum insolation is the factor introduced to explain the existence of the west winds. A second explanatory theory is discussed in which radiation from the cloud tops of the “intertropical convergence zone” locally reverses the equatorial solenoidal field to produce two new lines of convergence, one on each side of the equator. The same theory is the basis for a discussion of the rather complex structure of the intertropical convergence zones in each of which multiple lines of cloud build-ups are frequently observed. The paper also points out that the polar front is not to be identified with the high latitude zone of low pressure that appears in general circulation schemes, but rather that the front lies well equatorward from the low pressure zone as a result of topographical irregularities which, in turn, cause traveling disturbances, the low pressure centers of which fall well within the cold air on the poleward side of the statistical latitude of the polar front.