Global structure of longitudinal variations in the equatorial anomaly of ionospheric F2-layer Original Research Article

The main aim of the present report is to answer the question how many longitudinal periods actually exist in the equatorial anomaly of the ionospheric F2-layer. With this aim in view, by using ISS-b satellite data, a world-wide map of the equatorial-anomaly development in terms of the specially-introduced parameter P was drawn for the entire ranges of time and longitude. The basic conclusion of our study is that in the years of high solar activity there is only one or two clearly-expressed large-scale longitudinal periods of the equatorial anomaly corresponding to the local noon, and this number increases to three—five periods in evening and nighttime hours of Local Time. This conclusion turns out to be in a good agreement with earlier studies by Hopkins on the frequency of occurrence of the equatorial anomaly. The results obtained may be useful for verification and improvement of the IRI model.