Hourly insolation and meteorological data bases including improved direct insolation estimates. Final report

A new procedure has been developed to estimate hourly direct-normal insolation values from hourly total-hemispheric insolation values. This procedure is based on more than 20,000 simultaneous observations of these two quantities obtained since September of 1974 using carefully calibrated instruments at four different United States locations with widely differing climates. The model includes statistical variation of the estimated direct insolation values for a given hemispheric insolation value. The accuracy of the model has been extensively studied and it has been determined that the annual mean daily direct insolation values are estimated to within 4%. This procedure has been employed to estimate hourly direct-normal insolation from the Standard Year Corrected total-hemispheric insolation values recently generated from historical insolation observations by the National Climatic Center for 27 United States locations. Because of uncertainties in the Standard Year Correction procedure, the annual mean daily direct-normal insolation values estimated from these data have a 10% uncertainty associated with them. New hourly data bases including total-hemispheric and direct-normal insolation with surface meteorological data have been prepared for these 27 locations in the SOLMET format. The time period is 1952 through 1975 for most locations. Monthly mean insolation values have been computed by years from thesemore » new data collections and are included in this report. For some locations the present estimates of direct insolation are up to 40% lower than previous estimates based on earlier procedures.« less