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Abstract

The shade-ring correction factor needed for measurements of diffuse irradiance at the Dead Sea averaged 1.41. Under normal near cloudless conditions, the anisotropy factor for sky radiance at the Dead Sea was in mid-winter 14% greater than that calculated on the basis of clear sky radiance distribution measured in central England, rising to a 28% excess in mid-summer. the relative strength of the circumsolar radiance calculated from the Dead Sea measurements was 1.54 compared with the value of 1.10 found to fit the data from nine other stations. the calculated angular width of the circumsolar zone at the Dead Sea, 0.63 radians, was, however, similar to that derived from data at other stations. Two possible reasons for the high degree of anisotropy are discussed. the correction factor was not influenced by the degree of cloud cover until over half the sky was clouded. On the very infrequent occasions of completely overcast skies the shade-ring factor averaged 1.16, agreeing with the value calculated solely on the basis of the geometric view factor. the error in measurement of diffuse irradiance at the Dead Sea caused by uncertainties in the value of the shade-ring correction was less than 5%, smaller than the uncertainty in the basic reference method of measurement.