Frequency distribution of daily clearness indices through generalized parameters

Noting that frequency distributions of clearness indices available in the literature are not applicable for all climates, the present article examines the suitability of a new parameter, K ̄ T , and a variable, K T , to depict generalized clearness index distributions. K ̄ T is a normalized monthly average daily clearness index, while K T is a normalized daily clearness index. These normalized clearness indices comprise maximum and minimum daily clearness indices ( K T,max and K T,min ), in a month, in addition to monthly average daily clearness index, K ̄ T , and daily clearness index, K T . Correlations have been developed to predict K T,max and K T,min needed, in the absence of data. The distributions, developed in terms of K T and K ̄ T have been suitably represented and tested over 70 locations, latitudes ranging from 8°N to 64°N. The daily clearness index values have been predicted within a standard deviation of 0.034 with the expressions developed in the present study.