Abstract:
The Variations of meteorological parameters have great effects on radio wave signals propagating through the troposphere. Proper planning of radio communication links, can be achieved by continuous studying of the atmosphere using refractivity profiles to provide baseline data that could be used to mitigate satellite communication outage before the onset of severe adverse hydrometeor environment. This research work investigated the stability of the atmosphere using refractivity profiles. The study involves the use of radio refractivity profiles at the surface and 100 m to characterize the diurnal and seasonal variation of the surface radio refractivity and also to estimate the effective earth radius (k-factor) which is used to characterize the propagation condition in order to determine the onset frequency of anomalous propagation. In addition, two years reanalysis data of atmospheric parameters (temperature, atmospheric pressure and relative humidity) at four synopses hour of the day with a resolution of 0.25 x 0.25 were obtained from European Center for Medium-range Weather Forecast (ECMWF) at 1000 hPa, 975 hPa, 950 hPa, 925 hPa, 900 hPa, 800 hPa, 700 hPa, 500 hPa, 400 hPa, 300 hPa, 200 hPa, 100 hPa, to estimate the Atmospheric Stability Indices (ASI) and the Tropospheric Refractivity Lifted Index (TRLI). The result on a seasonal basis shows that the value of refractivity is high during the rainy and low during the dry season, with super refraction dominating during the rainy season (almost 100% occurrence). It also shows that the value of refractivity at the surface is higher than the value at 100 m which implies that refractivity decreases with height. The trend in the variation of the Atmospheric Stability Indices Using Refractivity Profiles (ASIRRP) and Lifted Index (LI) shows that when LI is negative, ASIRRP is more negative, which implies that the atmosphere is unstable. When LI is positive, ASIRRP is less negative which implies that the atmosphere is more stable,
except in cases where significant water vapour is lifted to 500 hPa, whenever LI is positive ASIRRP is found to be negative which implies that the atmosphere is unstable.
