Long-Term Assessment of Secondary Radioclimatic Parameters in a Coastal Tropical Environment: Evidence of Persistent Super-Refraction and Elevated k-Factor for Terrestrial Wireless Link Design in Toru-Orua, Nigeria.

The secondary radioclimatic parameters play a crucial role in the performance,
reliability and design of the terrestrial wireless communication system especially
in the humid tropical regions where atmospheric components have great effects
on radiowave propagation. This research studies the temporal variation of
radioclimatic variables at Toru-Orua, a coastal community in the Niger-Delta
area of Nigeria, using eleven years (2015-2025) of hourly ERA5 reanalysis data.
The derivation of surface radio refractivity, vertical refractivity gradient,
effective earth radius factor, and geoclimatic factor was done using the ITU
procedure. The findings indicate that surface refractivity varies significantly on
a diurnal and seasonal basis and is mainly caused by thermodynamics in the
boundary-layers, availability of moisture, rainfall variability. Vertical
refractivity gradient is predominantly negative which implies that the dominance
of super-refraction and intermittent ducting, especially at night time, early
morning hours and at the beginning of the wet season. The derived actual Earth
radius factor is always larger than the standard ITU value of 4/3 with an average
annual value of 1.67, indicating that the assumed standard atmospheric
refraction is inappropriate for link design in Toru-Orua. The computed
geoclimatic factor exhibits weak seasonal variability between 5.8E-05 and 6.5E
05 with an annual mean of 6.18E-05, consistent with values reported for other
southern Nigerian coastal locations. In general, the results highlight the
increased vulnerability of terrestrial radio links in Toru-Orua to anomalous
propagation and increased fade margin requirements, emphasizing the need for
site-specific
radioclimatic characterization in network planning and
optimization across coastal tropical environments.