DIFFERENTIAL ANGSTROM MODEL FOR PREDICTING INSOLATION FROM HOURS OF SUNSHINE

The Ångstrom model for predicting insolation is limited in scope beacuse it gives equal weighting to sunshine hours recorded at any time of the day. The differential Ångstrom model presented in this paper removes this limitation and relates insolation, qj, in the jth hour to the sunshine duration, nj, of the same period by the equation: qj = aj + bj. By regression analysis of monthly data, the set of constants aj and bj for each hour of each month of the year can be determined. Thus, using the appropriate set of a and b regression coefficients, any sunshine data can be transformed to insolation. The sum of the equation over a day gives the daily insolation from which monthly means can be calculated. The method has been applied to the 1986 and 1988 sunshine data recorded at the University of Papua New Guinea to predict the observed insolation to within 3.5%. The differential Ångstrom method has applications in places which have much recorded data on hours of sunshine but have limited observed insolation data. © 1990.