LONGWAVE RADIATION MODELING IN MOUNTAINOUS ENVIRONMENTS

Hourly atmospheric longwave radiation (L down arrow) flux densities ob served at an alpine tundra site in southern British Columbia were comp ared to eight different L down arrow 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 bot h cloudless and cloudy sky conditions. Most models performed well, wit h the exception of the LeDrew model. Overall, the Idso-Jackson model w as superior. The results demonstrated that L down arrow could be relia bly estimated from air temperature alone, and challenged the accepted notion that L down arrow models do not work effectively in mountainous environments. Measured terrestrial longwave radiation (L up arrow) va ried according to the dictates of the Stefan-Boltzmann Law. Comparison s between measured L up arrow and surface (skin) temperature indicated that blackbody assumptions of surface emissivity were appropriate.