Evaluation and Derivation of Cloud-Cover Algorithms for Calculation of Surface Irradiance in Sub-Antarctic and Antarctic Environments

To investigate approaches for parameterizing cloud cover effects in models of surface irradiance, the daily-averaged and hourly irradiances measured at Palmer Station (64°46'S, 64°3'W), McMurdo Station (77°5l'S, 166°40'E) and Ushuaia (54°49'S, 68°19'W) between 1993 and 1997 were compared to irradiance values computed with a clear sky radiative transfer model in which nine empirical cloud-cover correction relationships were included. The cloud cover correction algorithms improved the simulated irradiance by factors of 3 and 3.7 for Palmer Station and Ushuaia, respectively, over the non-corrected irradiances. No single cloud cover correction algorithm worked consistently at the three sites. Therefore, a power function cloud cover correction algorithm was derived from comparisons between the observed spectrally-integrated irradiances and the simulated irradiances at the three locations. New coefficient values for the power function cloud cover correction algorithm for the spectrally-resolved irradiances were also derived at the three sites, and were found to be spectrally-neutral and to differ in magnitude. The general trends in the values obtained for the three sites provide an approach for generalizing cloud cover correction algorithm coefficients to other parts of the Antarctic. Received 19 December 2003, accepted 1 October 2004