The present work aims to quantify long-wave radiation incidentby the Brunt (1932), Brutsaert (1975), Idso and Jackson (1969), Satterlund(1979), Swinbank (1963) and Prata (1996) methods, consideringclassification of sky conditions to a tropical semi-deciduos forest of thesouthern amazon basin in northern Mato Grosso, Brazil, from 2007 to 2008. The sky conditions were defined by clearness index (L↓) (cloudy,partly cloudy and clear). Average annual of long-wave radiation incident(L↓) was higher when estimated by the Satterlund method (381.18 ± 36.49W m-2), and by the Brutsaert method (380.17 ± 36.19 W m-2). There wasseasonality in daily cycle of long-wave radiation incident with higher valuesduring the daytime and lower during the night. L↓ estimated by theSwinbank and Idso & Jackson methods were correlated with air temperatureand humidity. Average annual of L↓ estimated by Brunt and Satterlundmethods differed of L↓ estimated by other methods.
