Abstract
A study of the long-term variability; trend and characteristics of visibility in four zones of Nigeria was carried out. Visibility and other meteorological data from NOAA-NCDC and aerosol index data over Nigeria during 1984–2013 are analyzed using time series and simple regression model. There are significant decreasing trends for every region and season during the 30-years period; the fluctuations exhibited nearly similar pattern. The 30-year mean visibilities for the four zones (Sahel; North Central; Southern; and Coastal) were 13.8 ± 3.9; 14.3 ± 4.2; 13.6 ± 3.5 and 12.8 ± 3.1 km with decreasing trends at the rates of 0.08; 0.06; 0.02 and 0.02 km/year. In all the zones; visibilities were better in summer while worse in Harmattan (dry season). During summer visibility was best in Sahel and North-central; however; in Harmattan visibility was best in southern and coastal zones. It was best between May and June (17.6; 18.9; 16.6 and 15.1 km) with a second peak in September. The 30-year seasonal averages were 16.2 ± 2.1; 16.8 ± 2.4; 15.4 ± 1.8 and 14.0 ± 2.2 km in summer; and 10.2 ± 2.5; 10.9 ± 2.9; 11.0 ± 3.3 and 11.4 ± 3.0 km in Harmattan for the respective zones. Sahel and North Central had the worse visibility reduction during Harmattan compared with Southern and coastal areas. An analysis based on simple regression equation reveals a strong and negative relationship between visibility on one hand; AI; and AOD on the other hand. The analysis also discusses the variability regarding the frequency of occurrence of a dust storm; dust haze; and good visibility over the period of study.
Highlights
Visibility becomes one of the most current discussions in climatology and air quality studies; it is the most direct way to access the level of air pollution in any region of the world
The fact that trends changes in all season and zones indicates that anthropogenic emission and transport of aerosol occurs continuously in all season across Nigeria
The temporal trend, characteristics and variability of visibility over Nigeria has been investigated in this paper using a 30 years (1984–2013) period data
Summary
Visibility becomes one of the most current discussions in climatology and air quality studies; it is the most direct way to access the level of air pollution in any region of the world. Depending on the area of interest and application, visibility in meteorology is defined as maximum distance at which a dark object can be discerned against a light sky [1,2] on the other hand, it is defined in aviation as the greatest horizontal distance at which a large object can be seen and recognized against a bright sky [3]. It is different from vertical visibility determined based on measuring aerosol optical depth from satellite images [4]. Visibility can be influenced by Geographical and meteorological conditions of an area
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