SPATIAL DISTRIBUTION OF HARMATTAN DUST (AEROSOL) LOADING ON HORIZONTAL VISIBILITY OVER NORTHERN NIGERIA

Abstract

A study on the Spatial Distribution of Harmattan Dust (Aerosol) Loading on Horizontal Visibility over Northern (lat. 80N-140N and long. 30E-150E) Nigeria was carried using thirty (30) years visibility, Community Earth System Model Aerosol Optical Depth (CESM AOD) and Spatial pattern of near surface (925hpa) wind field for the month of November -March. Twelve (12) stations were considered in this research based on the availability of horizontal visibility data for the research period. The study aims at analyzing the spatial distribution of harmattan dust (aerosol) loading on horizontal visibility over the study area during the period of thirty (30) years. The spatial distribution of harmattan dust haze over the region was obtained using the inverse distance weighted method from the from the spatial analytical tool on Arch GIS to pict the distribution pattern of the CESM AOD. The spatial pattern of near surface wind field over the Northern, Nigeria was determined using Era-Interim Reanalysis datasets for the daily mean Zonal U and Meridional V components. The horizontal visibility data obtained from Nigerian Meteorological Agency (NIMET) was also computed to depict the variation over the period. The mean monthly visibility peaks in the month of March and decreases significantly again with corresponding increase in CESM AOD across the selected station. Aerosol build up begin in the month of November and continues across the months which peak in January and thereafter begins to decline across the months. Visibility is seen to be higher in November with a lower Aerosol and reduces across the months with increasing aerosol. The average visibility mean (Geographical mean) for the 30 years is found to be approximately 12.64km across the study area, with Kebbi state (Nguru) having the highest visibility (19.5km) and Abuja the least visibility (7.64km). The Station visibility is generally lower than the average visibility (Geographical mean) across the study areas