Longwave sky radiation parametrizations

Abstract New empirical models for predicting daily mean thermal radiation from both clear and cloudy skies are proposed. Their great advantage is that they only use the three following variables, which can be measured easily by an automatic weather station at the ground level: the air temperature, the water vapor pressure, and the clearness index. In particular, neither cloud cover measurement nor temperature or humidity profiles are needed. The models are adjusted to measurements carried out in Gembloux, a town 40 km away from Brussels, Belgium. The most elementary model, based solely on the water vapor pressure, gives already reasonable estimations with a correlation coefficient 0.914. The best model is based on all three variables with a correlation coefficient of 0.958.