Temporal Analysis of Radio Refractivity Variation over Kaduna: Implications for Radio Wave Communication Systems

Abstract

Study’s Excerpt:
• Refractivity in Nigeria’s savannah is stable yearly (±13 N) but swings monthly (112 N) with wet/dry seasons.
• Humidity, not temperature, drives refractivity peaks (391 N) in October rains, setting a new regional record.
• ERA5 data is valid for West African refractivity, bridging ground data gaps for climate-based models.
• Guides adaptive systems (antenna/power tuning) to boost telecom planning in Nigeria’s savannah zones.
• Kaduna’s refractivity aligns with rainforest, not savannah, challenging assumptions on regional propagation.
Full Abstract:

Surface radio refractivity is a crucial parameter in studying radio wave communication as it quantifies the bending of electromagnetic waves by atmospheric factors. This study examines the temporal variations of this parameter in tropical savannah region of Kaduna, Nigeria, for a long time. Accurate measurements of temperature, atmospheric pressure, and relative humidity extracted from high-resolution meteorological data from the ECMWF ERA5 reanalysis dataset were used to perform this research. The radio refractivity is computed using ITU-recommended models integrating these variables to express radio refractivity in N-units, which is a global standard for values comparison. The analysis revealed that yearly mean refractivity remained notably stable, fluctuating between 340.0565 and 353.4296 N-units, a modest range of 13.3731 N-units across four decades. This stability points out how easily atmospheric conditions can be predicted in long-term communication planning in Kaduna. On the other hand monthly radio refractivity show high variability ranging from 279.0400 N-units in March 1990 to 391.5037 N-units in October 1997—a difference of 112.4637 N-units. This variability originated from the wet and dry seasons of the location of the study. Higher radio refractivity values during the rainy season indicate a sharp increase in water vapour pressure and humidity, while lower refractivity values mark the dry season. These results indicate the necessity of utilising local climate conditions when studying electromagnetic wave propagation and fill a critical gap in long-term refractivity research, especially in tropical savannah areas.