Radiative cooling computed for model atmospheres.

Calculations of spectral radiance are reported from several model atmospheres appropriate to different climatic conditions by use of the LOWTRAN 5 computer code. From these data we evaluate the radiative cooling power and the temperature drop below ambient temperature for horizontal surfaces that radiate toward the sky. The surfaces are ideal blackbodies or have ideal infrared-selective properties with zero reflectance in the 8-13-microm range and unity reflectance elsewhere. For freely radiating surfaces, the cooling power at ambient temperature lies between 58 Wm(-2) and 113 Wm(-2) for the different surfaces and model atmospheres. The maximum temperature difference for a device with a nonradiative heat transfer coefficient of 1 Wm(-2) K(-1) is between 11 and 21 degrees C for a blackbody and between 18 and 33 degrees C for an infrared-selective surface. For radiators arranged so that they intercept only the atmospheric zenith radiance, the cooling powers and temperature differences are higher than for freely radiating surfaces, the increase being largest for humid atmospheres. The influence of altered contents of water vapor was found to affect strongly the radiative cooling, whereas changes in ozone and aerosol abundance were less important. The significance of these results to different cooling applications is briefly discussed.