Retrospective on the resource for radiative cooling

Abstract

The history of quantitative measurements of radiative cooling is briefly reviewed, starting with Count Rumford in 1804. The cooling results from upward emission of thermal infrared radiation (wavelengths of 5 to 50 μm) that is not fully offset by downward atmospheric emission. The downward emission is characterized by the apparent atmospheric (sky) emit-tance and the surface air temperature. In 1984, an equation was published that describes the clear sky emittance as a function of the surface dew point temperature. At the time, this equation was merely one of many empirical relations. Now that time has passed, experimental and theoretical advances support its validity. Further refinements can include improved corrections for time-of-day and the lower air pressure at elevated locations. Complex computer codes for predicting atmospheric radiation have reached quantitative maturity. Given profiles of air temperature , water vapor, CO 2 , O 3 , CH 4 , N 2 O, and aerosols, they can compute spectral radiances with an accuracy of ∼3%. The effect of clouds in reducing radiative cooling remains more uncertain.