Comparison of surface radiative flux parameterizations - Part I: Longwave radiation

This paper presents a comparison of several longwave (LW) downwelling radia tive flux parameterizations with hourly averaged pointwise surface-radiatio n observations made at Sodankyla, Finland, in 1997 and 1999. Both clear and cloudy nighttime conditions are considered. The comparisons covered a 2-m temperature range from +11 degreesC all the way to -49 degreesC. The clear-sky comparisons included eight simple LW parameterizations, which mainly use screen-level input data, and four radiation schemes from numeri cal weather prediction (NWP) models: the former European Centre for Medium- Range Weather Forecast (ECMWF) scheme, the Deutscher Wetterdienst (DWD) sch eme, the High Resolution Limited Area Model (HIRLAM) scheme, and the new EC MWF LW scheme (Rapid Radiative Transfer Model, RRTM). Atmospheric-sounding profiles were used as input for the NWP schemes. For the cases with clouds, three simple cloud-correction methods were tested. Almost all LW schemes usually underestimated the downwelling clear-sky flux , particularly, in cold (surface inversion) conditions. Overall, the RRTM s cheme performed best. The simple cloud-correction methods turned out to be useful in the LW region. Finally, some new simple parameterization formulas were developed using the present data. (C) 2001 Elsevier Science B.V. All rights reserved.