EFFECTS OF COUPLED OCEAN-ATMOSPHERE PHENOMENA ON COMMUNICATION SYSTEMS OVER AFRICA

Abstract

The pathway of propagated radio waves is partly determined by the refractive index of the atmosphere through which the waves traverse. Significant influence on radio wave propagation can be as a result of changes in atmospheric parameters (temperature, humidity and water vapor partial pressure) leading to changes in the atmospheric refractive index. In this study, the effects of coupled ocean-atmosphere phenomena on radio communication systems over Africa are investigated. Sixty years (1950 – 2010) reanalysis daily satellite data of surface atmospheric parameters and the data set for the oceanic indices (El Nino Southern Oscillation, Northern Atlantic Oscillation, Pacific Decadal Oscillation, Tropical South Atlantic and Tropical North Atlantic) were obtained from National Oceanic and Atmospheric Administration (NOAA) and the archive of the European Centre for Medium-Range Weather Forecasts (ECMWF) respectively and were utilized. The data spanned across African continent on the resolution of 0.25 o x 0.25 o . The surface radio refractivity was computed from the atmospheric parameters. Detailed statistical analysis at significant level of P < 0.05 involving time series, linear correlation, causality test and Regression have been carried out between oceanic indices, radio refractivity and atmospheric parameters. The results show that the mean value of temperature across Africa varies from 284 to 302 K with the highest value at the Sahel region. Surface pressure varied latitudinally from the Equator to the Northern region of Africa. The variation of the mean value of surface radio refractivity over Africa ranges from 160 to 400 N-units. Meanwhile, the variation of surface radio refractivity reduces from the tropical region towards the Northern Africa region, but is high at all coastal regions of Africa. Desert region, Rainforest region and Steppe region of Africa exhibited the same surface radio refractivity distribution pattern viiwith a minimum value between 290 and 298 N-units and maximum values between 323 and 332 N-units. The oceanic indices exhibited cyclic pattern with different frequencies of occurrence. Significant but predominantly weak correlation (-0.25 – 0.25) between oceanic indices and atmospheric parameters resulted in weak correlation relationship between radio refractivity and the oceanic indices. The North Atlantic Oscillation (NAO) exhibited latitudinal correlation with surface radio refractivity. Consequently, information and value of radio refractivity can be obtained with knowledge of the event of NAO at about 70% of the African continent. An increase in the value of the oceanic indices such as NAO corresponds to average of 1 to 6 N-units reduction in the value of surface radio refractivity. The result offers the opportunity to predict fluctuations in surface radio refractivity through the event of oceanic indices in other to plan for better radio communication system.