Refinement and Testing of the Radiative Transfer Parameterization in the PL Global Spectral Model
PHILLIPS LAB HANSCOM AFB MA
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As part of a larger initiative to develop a research-grade advanced physics global spectral numerical weather prediction model, an atmospheric radiative transfer parameterization scheme that interacts with model clouds has been developed. It has been incorporated into the Phillips Laboratory PL global spectral model along with state-of-the-art schemes to account for boundary layer exchange process, cumulus convections and gravity wave drag. The radiation scheme employs a broadband approach to account for longwave and shortwave fluxes in clear and cloudy atmospheres. For cloud regions, up to three cloud decks can be handled, corresponding to low, middle, and high clouds. Several procedures to transform the models distribution of relative humidity at each gridpoint to the three deck cloud solution were evaluated. A variation of the so-called Slingo scheme employed in the global model of the European Centre of Medium-range Weather Forecasting was selected. The radiation flux calculations proceed with one of seven possible cloud layer scenarios and use maximum overlap assumptions. Global model experiments with the cloud-radiation scheme confirmed the successful simulation of observed outgoing longwave radiation from satellite observations both in its magnitude and in the proper placement geographically of extrema. Improvements in the global model heating rate profiles resulted, in turn, in improved temperature forecasts throughout the model tropospherestratosphere.