A STUDY OF THE DIVISION OF GLOBAL IRRADIANCE INTO DIRECT BEAM AND DIFFUSE IRRADIANCE AT 7 CANADIAN SITES

Canadian hourly global and diffuse irradiation data and associated dai ly surface meterological data of humidity, temperature and snow depth for the years 1977-1984 are analyzed. These data have been measured at Edmonton, Goose Bay, Montreal, Port Hardy, Resolute, Toronto and Winn ipeg. Hourly values of the clearness index k(t) and diffuse index k(d) are sorted into bivariate histograms according to their numerical val ues. Different histograms are established for different ranges of the three variables: solar elevation, atmospheric precipitable water, and snow depth for each station. Properties of the different histograms ar e compared using standard statistical procedures. It is found that the division of global irradiation into direct beam and diffuse irradiati on is correlated with the four variables K-t, precipitable water, sola r elevation, and snow depth. II is also found that many, but not all, of the differences between data from the same station at different tim es and between different stations can be attributed to conditions asso ciated with differences in these four variables. The data show evidenc e that the division of global irradiation into direct and diffuse irra diation can depend upon the properties of the clouds beyond how these clouds are characterized by the four variables.