Evaluation of effective atmospheric emissivity and parameterization of cloud at local scale

We have measured the radiation components continuously over a partially cheatgrass-covered area since October 1995 and compared the measured incoming longwave (atmospheric) radiation with that computed by Brutsaertʹs formula. Data analysis showed very good agreement between the measured and computed atmospheric radiation during cloudless periods. During cloudy conditions the measured atmospheric radiation is greater than that computed by Brutsaertʹs formula. The additional longwave radiation during the cloudy skies comes from clouds in the waveband which the gaseous emission lacks, i.e. from 8 to 13 μm (the so-called atmospheric window). We proposed an approach which uses the thermodynamic concepts and some climatic parameters to parameterize cloud at local scale. Based upon the proposed method, the cloud base height, cloud base temperature, and percent of sky covered by cloud can be evaluated continuously for any location without introducing any empirical and local constants.