EFFECT OF AEROSOLS ON SOLAR IRRADIANCE OVER ILORIN, NIGERIA.

Abstract

This study investigated the annual variation of surface solar irradiance during 1998 – 2012 over Ilorin city as well as their relationships to Aerosol Optical Depth (AOD) under both clear and all-sky conditions. Two periods with unique features of long term variation of solar irradiance were identified for both clear-sky and all-sky conditions: a dimming period the late 1998 to the mid 2004, and a brightening period from the mid 2004 to 2012. During the two periods of solar radiations, a significant brightening was observed from the year 2000 under both clear – sky and all – sky conditions, indicating that change in atmospheric transparency resulting from aerosol emission has an important role on annual variation of surface solar radiation (SSR) under this area. The analysis on the relationship between the Aerosol Network (AERONET) retrieved AOD and the corresponding monthly mean measurement of solar radiation fluxes under both clear – sky and all – sky conditions revealed that, AOD is significantly correlated with the radiations parameters under all-sky conditions, and anti-correlated with clear-sky radiative parameters, both above 99% confidence, indicating the great impact of ambient aerosol on solar irradiance through absorption and scattering in the atmosphere. In addition, aerosols loading which are generated by intense Saharan dust outbreaks and occasionally biomass-burning activities in the region, showed minimal presence between the months of December to August and maximal attendance during the months of September to November. This is attributed to the gradient of increasing precipitation and the location of source regions for the dust. The study provides useful information on the effect of aerosols on solar radiation for climate change studies under different weather conditions, which will be useful for governmental agencies such as aviation industry, thereby making appropriate policies and decision for making accurate weather forecast in related atmospheric models.