Burgette A. Hart, G. D. Thayer, and Harold T. Dougherty

Abstract: Telecommunication technology and its applications are rapidly expanding in the new or developing nations, many of which are located in tropical climates; so a knowledge of the behavior of refractivity gradients, directly related to establishing and maintaining reliable communication circuits, is especially important in this region. The distribution and variability of ground-based radio refractivity gradients in tropical areas of the world are quite different from those found in temperate climates where the annual range of daily mean temperature is much larger than the daily temperature range. Examples of them refractivity vertical structure in locations from 30*N to 30* S, are presented to show that very large diurnal and interdiurnal fluctuations in surface gradients are the rule rather than the expectation. These fluctuations, only slightly affected by seasonal cycles, are largely dependent on diurnal isolation and local features, such as terrain, prevailing winds and moisture sources. Improved observational techniques and a careful study of local climactic effects can result in more accurate prediction methods for better telecommunication system design.

Keywords: propagation; refractive gradient analysis

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