Clear Skies at Sebele, Botswana

J. Andringa


The distribution of the clearness index at Sebele, Botswana, ispresentedfor the period 1977 to 1992. Botswana lies in the mid-latitudes. between the tropical and temperate zones. Additionally the country has a semi-arid savannah-like climate. The monthly means of the daily clearness index KAvG are behveen 44% and 7S%. When the averages of the monthly means of K,, (K )are taken for each month, it is noted that these clearness indices range from 57% to 68%. During the rainy season, relatively low values of the clearness index KAY, are experienced. In the winter period, the cumulative
frequency distribution of the clearness index is relatively high for the months of May, June, July and August.

The maximum value of the monthly average clearness index K,. has been calculated by many researchers using expressions based on K, only. In this paper it is shown that the method used by Hollands and Huger produces results that show a better correspondence to the observed data for Botswana than the method of Saunier.

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