PERFORMANCE OF GLOBAL TO DIRECT DIFFUSE DECOMPOSITION MODELS BEFORE AND AFTER THE ERUPTION OF MT-PINATUBO, JUNE 1991/

Different decomposition models have been developed to estimate hourly direct and diffuse solar irradiance from hourly global irradiance meas urements. Besides clearness index k(t), other geometric and meteorolog ical variables have been tested as predictors of hourly diffuse fracti on, k, or hourly beam transmittance index, k(b), by means of piecewise correlations. The recent volcanic eruption of Mount Pinatubo (June 19 91) was responsible for important modifications in the solar radiation fluxes. In this article we address the effect of the volcanic aerosol s on the performance of some well-known empirical models, using a data set including different radiometric and meteorological variables. The study has revealed that the more pronounced performance changes affec ted the higher k(t) intervals associated with the lower levels of clou d cover. After the eruption, all the models present a general tendency to overestimate the direct component and underestimate the diffuse co mponent. Copyright (C) 1997 Elsevier Science Ltd.