A comprehensive study on the anomalous propagation (AP) conditions occurring over the central and west African stations was made from 2 years (January 2005–December 2006) high-resolution data measured by GPS (Global Positioning System) radio survey observations. Through data quality control and diagnostic analysis, the probability of AP occurrence and characteristic quantities of the three typical anomalous propagation conditions were given. The sub-refraction, super-refraction and ducting cases were investigated statistically using the vertical profile of modified refractivity gradient. Strong diurnal variation in the percentage occurrence of the AP had its peak during the wet months, while the dry months had the lowest values. From 0600 to 1800 local time (LT) at day (1800–0600 LT at night), the total percentage occurrence of super-refraction, sub-refraction and ducting were 82.5% (78.5%), 11% (15.5%) and 6.5% (6%), respectively. Besides statistical results, local meteorological conditions prevailing over central and west Africa have also been discussed.
$\bullet$ Seasonal maps of occurrence of sub-refraction, super-refraction and ducting layers have been constructed.
$\bullet$ The daytime (0006–1800 local time) is seldom affected by ducting as a result of the ceaseless and intense heat activity.
$\bullet$ The refractivity index was obtained from in-situ measurements performed at the 19 stations.
$\bullet$ Sub-refractive prevails at daytime whereas super-refractive and ducting are observed at night time (1800–0006 local time).
Volume 129, 2020
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