Initial Analyses of Surface Spectral Radiance Between Observations and Line-by-Line Calculations

The evaluation and improvement of radiative transfer calculations are essential to attain improved performance of general circulation models (GCMs) for climate change applications. A Quality Measurement Experiment (QME) is being conducted to analyze the spectral residuals between the downwelling longwave radiance measured by the University of Wisconsin Atmospheric Emitted Radiance Interferometer (AERI) and spectral radiance calculated by the Line-By-Line Radiative Transfer Model (LBLRTM). The three critical components of this study are 1) the assessment of the quality of the high resolution AERI measurements, 2) the assessment of the ability to define the atmospheric state in the radiating column, and 3) the evaluation of the capability of LBLRTM. Validations have been performed on spectral radiance data, obtained from April 1994 through July 1994, through the analysis of the spectral residual differences between measured and calculated radiances. These residuals are analyzed by both spectral interval and physical process. The results are archived as a function of time, enabling the retrieval of specific data and facilitating investigations of diurnal effects, seasonal effects, and longer-term trends. While the initial focus is restricted to clear-sky analyses, efforts are under way to include the effects of clouds and aerosols. Plans are well formulated for the extension of the current approach to the shortwave. An overview of the concept of the QME is described by Miller et al. (1994), and a detailed description of this study is provided by Clough et al. (1994).