The Cryosphere www.the-cryosphere.net 1994-0416 1994-0424 3 1 2009 10.5194/tc-3-75-2009 http://www.the-cryosphere.net/3/75/2009/ http://www.the-cryosphere.net/3/75/2009/tc-3-75-2009.html http://www.the-cryosphere.net/3/75/2009/tc-3-75-2009.pdf 75 84 2009-04-27 Testing longwave radiation parameterizations under clear and overcast skies at Storglaciären, Sweden J. Sedlar josephs@misu.su.se R. Hock Department of Meteorology, Stockholm University, 106 91 Stockholm, Sweden Geophysical Institute, University of Alaska Fairbanks, AK 99775-7320, USA Department of Earth Sciences, Uppsala University, 752 36 Uppsala, Sweden Energy balance based glacier melt models require accurate estimates of incoming longwave radiation but direct measurements are often not available. Multi-year near-surface meteorological data from Storglaciären, Northern Sweden, were used to evaluate commonly used longwave radiation parameterizations in a glacier environment under clear-sky and all-sky conditions. Parameterizations depending solely on air temperature performed worse than those which include water vapor pressure. All models tended to overestimate incoming longwave radiation during periods of low longwave radiation, while incoming longwave was underestimated when radiation was high. Under all-sky conditions root mean square error (RMSE) and mean bias error (MBE) were 17 to 20 W m^−2 and −5 to 1 W m^−2, respectively. Two attempts were made to circumvent the need of cloud cover data. First cloud fraction was parameterized as a function of the ratio, τ, of measured incoming shortwave radiation and calculated top of atmosphere radiation. Second, τ was related directly to the cloud factor (i.e. the increase in sky emissivity due to clouds). 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