Assessment of clear and cloudy sky parameterizations for daily downwelling longwave radiation over different land surfaces in Florida, USA

Clear sky downwelling longwave radiation (R ldc ) and cloudy sky downwelling longwave radiation (R ld ) formulas were tested across eleven sites in Florida. The Brunt equation, using air vapor pressure and temperature measurements, provides the best R ldc estimates with a root mean square error of less than around 12 Wm −2 across all sites. The Crawford and Duchon's cloudiness factor with Brunt equation is recommended for R ld calculations. This combined approach requires no local calibration and estimates R ld with a root mean square error of less than around 13 Wm −2 and squared correlation coefficients that typically exceed 0.9.