LONGWAVE RADIATION MODELING IN MOUNTAINOUS ENVIRONMENTS

Abstract

Hourly atmospheric longwave radiation (L↓) flux densities observed at an alpine tundra site in southern British Columbia were compared to eight different L↓ models that utilized screen-level temperature and/or vapor pressure input data. Models tested were the Stefan-Boltzmann equation using an effective atmospheric emissivity of .70, and the models formulated by Brunt, LeDrew, Swinbank, Idso, Idso-Jackson, Brutsaert, and Berdahl-Martin. All models were tested on both cloudless and cloudy sky conditions. Most models performed well, with the exception of the LeDrew model. Overall, the Idso-Jackson model was superior. The results demonstrated that L↓ could be reliably estimated from air temperature alone, and challenged the accepted notion that L↓ models do not work effectively in mountainous environments. Measured terrestrial longwave radiation (L↑) varied according to the dictates of the Stefan-Boltzmann Law. Comparisons between measured L↑ and surface (skin) temperature indicated that blackbody assumptions of surface emissivity were appropriate. [Key words: climatology, longwave radiation, alpine tundra, British Columbia.]