Estimation of beam solar fraction at normal incidence transmitted on terrestrial surface as function of clearness index and of insolation ratio - Santos, Cícero Manoel dos; Escobedo, João Francisco; Dal Pai, Alexandre; Oliveira, Amauri Pereira de; Soares, Jacyra Ramos (São Paulo Spring School on Urban Climate at Tropical Regions: Observational and Modeling Features, 2013)