This page evaluates the ecRad implementation of the RRTMG gas optics scheme operational in the ECMWF model. It is indistinguishable from version 3.9 of RRTMG available from AER. RRTMG is designed for weather and climate applications. The comparisons below use the 50 profiles of the "Evaluation-1" CKDMIP dataset. The reference calculations were performed using LBLRTM to generate the high resolution absorption spectra and the CKDMIP software to perform the radiative transfer. This page should be compared to the RRTMGP comparisonevaluation, where RRTMGP is an updated version of RRTMG.
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The shortwave RRTMG gas optics scheme uses a total of 112 g-points (k terms) in 14 bands. The following plots evaluate fluxes and heating rates for the four CKDMIP greenhouse-gas scenarios "Present", "Preindustrial", "Glacial Maximum" and "Future". Five solar zenith angles have been used with a fixed surface albedo of 0.15, the approximate global-mean value. The blue lines show the "raw" results from RRTMG, but since it is known that the solar spectrum is somewhat outdated in RRTMG, the fluxes in each of the 13 "narrow" CKDMIP bands have been scaled to match the more up-to-date solar spectrum used in CKDMIP - these results are in red. It can be seen that this correction substantially improves the agreement with the reference calculations.
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