Abstract
The aim of this paper is to estimate the mean monthly values of clearness index in five meteorological stations in Iraq (Mosul , Kirkuk , Rutba , Baghdad , Nasiriya) for the period (1970-2000) using different meteorological parameters. Five different models (Linear , Quadratic , Logarithmic , Linear logarithmic , Power) were used to estimate clearness index. The performance of this regression models were evaluated by comparing the calculated clearness index and the measured clearness index . Several statistical tests were used to control the validation and goodness of the regression models in terms of correlation coefficient, coefficient of determination , Mean absolute error and root mean square error . Results showed that Linear model between (KT & n/N) and between (KT & Rainfall) were the best fit in all stations. Quadratic model were the best fit between (KT & cloudiness) , and power model were the best fit between (KT &Evaporation). Linear model and Quadratic model were the best fit between (KT & RH) , while power model , Quadratic model , and Linear model were the best fit between (KT & Tmean).
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