Abstract
Aerosol Index (AI) values from the TOMS instrument were used to compute AI climatology in Africa north of the equator and in the Saudi Arabian desert (30°W-60°E, 0°-50°), for the period 1979-1992. Monthly and annual averages are presented for the whole area as well as for 9 other source areas.
The highest AI values were found in the summer months of May, June and July. The area around lake Chad has the highest value and, contrary to the other sources, is active throughout the year. The first 4 years of the research period has a significantly lower index value as compared with the later years. There is a sharp discontinuity between the years 1982 and 1983 in the western sources and a more moderate increase in the eastern sources. Two periods with very high AI values are identified, namely 1983-1984 and 1987-1988, while the year 1986 had a low index value. In 1991 and, to a lesser extent, in 1992, very high AI values were obtained in the eastern sources.
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