Solar Radiation Climatology of Alaska
Dorte Dissing and Gerd Wendler
Geophysical Institute, University of Alaska Fairbanks, Alaska 99775
There are only 6 locations in Alaska for which global radiation data are available for more than a year in duration. This is an extremely sparse coverage for a state of Alaska's size; 1.53x106 km2 and stretching over at least three climatic zones. Cloud observations are, however, available from 18 stations. We utilized fractional cloud cover and cloud type data to model the global radiation and thus obtain a more complete coverage of Alaska. This extended data set also allowed an analysis of geographic and seasonal trends.
A simple 1-layer model based on Haurwitz's semi-empirical model, allowing for changing cloud types and fractional coverage, was developed. The model predicts the annual global radiation fluxes to within 2-11 % of the observed values. Estimated monthly mean values gave an average accuracy of about 6 % of the measurements. The estimates agree with the observations during the first third of the year but less so for the last third. Changing surface albedo might be the culprit.
Previously, the 1993 National Solar Radiation Data Base (NSRDB) from the National Renewable Energy Laboratory (NREL) modeled global radiation data for 16 Alaskan stations. Although more complete and complex, the NREL model needed a larger number of variables as input, which were not available in Alaska. Hence, we believe that our model, which is based on cloud-radiation relationship and is specifically tuned to Alaskan conditions, produce the better results for this region. Contour plots of seasonal and mean annual spatial distribution of global radiation for Alaska are presented and discussed in the context of their climatic and geographic settings.
Financial support was obtained from the State of Alaska under a grant to the University of Alaska.
1998, Theoretical and Applied Climatology, Vol 61(3,4), 161-175.
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