SPATIO -TEMPORAL VARIATION OF HARMATTAN DUST HAZE OVER NIGERIA

Abstract

The study has assessed the spatial and temporal variations of harmattan dust haze in Nigeria. Daily visibility data on occurrence of thick dust haze (TDH) and light dust haze (LDH) covering a period of thirty years (1980–2009) for 16 synoptic stations fairly representing the four climatic zones in Nigeria during dry season (November-February) were collected from the Nigerian Meteorological Services, Oshodi, Lagos. Aerosol Optical depth (AOD) data was obtained from the AERONET ground-based spectrometer for 2004–2009 at Ilorin and was use to validate the horizontal visibility. The data were used to determine the frequency of occurrence of TDH and LDH during Harmattan season; examine the spatial variation in seasonal occurrence of TDH and LDH over Nigeria; and investigate the relationship between TDH/LDH with latitude. Analysis were carried out using descriptive statistics, co-efficient of variation, correlation/correlation coefficient and probability of occurrence over region. The results of the analysis show that the main natural causes of harmattan dust haze in Nigeria is the source region (Sahara desert), and the major factors determining this distribution of TDH and LDH are attributed to distance from dust source region, decrease in dust particle size and wind speed from north to south, increase in atmospheric humidity and vegetation cover from the Sahel in the north to the coastal zone in the south. Also, this study evaluated visibility data against ground-based spectrometer over Ilorin and found that AOD increases as the visibility decreases with a strong correlation coefficients of 0.5, based on the correlation, visibility data can reasonably be used to reproduce dust haze measurement over Nigeria. The dependence of the measures of variability on latitude is quantified by correlation analysis and results show that TDH depends on latitude with a positive correlation coefficient of 0.3, while the LDH decreases with latitude over the region with a negative correlation coefficient of -0.4, which is less depend on latitude.