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- 8c25b822-ad70-4e0f-b453-97fe5a80ae1f definition "The fourth intercomparison is actually one of the earliest conducted by DOE. ICRCCM is a program co-sponsored by DOE, the World Meteorological Organization (WMO), and the International Radiation Commission (IRC). The late Fred Luther gave the best description of the rationale for the program: 'Since the transfer of solar and longwave radiation is the prime physical process that drives the circulation of the atmosphere and its temperature structure, it is natural that an evaluation of the modeling of physical processes important to climate begin with radiation.' (Luther 1984) Principal Findings: 1. Line-by-line models are in good agreement with each other to within a few W/m2 (usually within 1%) when arbitrary line width cutoffs are universally applied. The ICRCCM concluded that: 'Uncertainties in the physics of line wings and in the proper treatment of the continuum make it impossible for line-by-line models to provide an absolute reference . . .' (Luther et al. 1988). Thus, no present-day model furnishes a reliable standard by which to judge other models, nor are appropriate data available. 2. There is no systematic difference between wide-band and narrow-band model results. However, there is a large variation among the band models. While average differences from line-by-line results range from 5 to 10%, the spread among the band models is several times larger. 3. Band model calculations of sensitivities to changes in absorbing constituents show poorer agreement with line-by-line results, and a much larger spread, than calculations of flux components. For example, when is doubled, the median band model sensitivities differ by up to 18% from line-by-line values, while their spread is an order of magnitude larger. 4. In cases of only and only, the spread in results among band models increases considerably compared to the case when all absorbing gases are included; this indicates that the success in the latter case is partly fortuitous because of the way absorbing bands overlap in the Earth's atmosphere. 5. For the longwave clear cases, with about 40 participants representing almost all the world's major modeling groups, ICRCCM revealed intermodel disagreements in fluxes and flux sensitivity to constituent changes ranging from 30 to 70% (Luther et al. 1988). The disagreements are worst for single absorbing gas atmospheres, indicating that the better agreement found in the all-gas cases is partly accidental. Subsequent ICRCCM calculations, involving cloudy longwave cases, and clear and cloudy shortwave cases, have revealed equally large or larger disagreements, ranging up to 20 to 30% in fluxes and up to 70% in flux sensitivity to constituent changes. 6. Comparisons are still in progress for vertical profiles of radiative heating rates. Disagreements in radiative heating rates are expected to be larger than for fluxes, because heating rate is the derivative of flux and taking derivatives magnifies errors For more information, link to 'http://www.arm.gov/docs/documents/project/er_0441/bkground_5/radcompar_9.html'" @default.
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