Equatorial anomaly in F-region—A Review

225-240The current knowledge of the equatorial anomaly in the electron density distribution of the ionospheric F-region is reviewed with emphasis on issues relevant to the quantitative modellingof the phenomena. The basic physical mechanisms responsible for the formation, development and decay of the anomaly and their mutually interactive nature are first outlines, followed by a brief discussion of the relevance of the anomaly to other characteristics of the equatorial low latitude ionosphere. Salient features of the schemes adopted for numerical simulation of the anomaly and the inputs required for the same are discussed. The inadequacy of the currently available global models of the input parameters is pointed out through some of the recent experimental results. The need for developing reliable data bases of the key parameters of the ionosphere-thermosphere system from systematic, extensive and simultaneous multi-technique/multi-station observations on a regional/global basis for a comprehensive understanding of the anomaly is highlighted