Atmospheric transparency under harmattan condition

Abstract

Results of preliminary investigations of the transparency of the atmosphere to direct solar irradiance under two typical harmattan conditions in Akure (7°18'N, 5°15'E) in the spectral interval, 300-1100 nm, are presented for cloud-free conditions. The meteorological effects of the north-south movement of the Inter-Tropical Discontinuity (ITD) during the season over the station has been related to the observed changes in the spectral transmittance. It has been shown, that solar energy arriving at the earth's surface could decrease as much by as 15% of the energy available at the top of the atmosphere within two harmattan regimes. Transmittance characteristics of some spectral bands influenced by water vapour absorption has been used to show that the precipitable water vapour aloft becomes smaller as spell conditions succeed background harmattan conditions at a station. The transmittance of the atmosphere to the direct solar radiation has therefore been shown as being capable of providing useful insights into the drastic changes that could occur in the precipitable water vapour in the atmosphere as the ITD passes over a station. .

Ife Journal of Science Vol. 8 (2) 2006: pp. 141-148