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The longwave gas optics scheme uses a total of 256 g-points (k terms) in 16 bands. The evaluation has been performed using radiative transfer with four zenith angles in each hemisphere (8-stream). The following plots evaluate fluxes and heating rates for the four CKDMIP greenhouse-gas scenarios "Present", "Preindustrial", "Glacial Maximum" and "Future". The comparison shares some of the features of the ecRad-RRTMG results, but are generally improved with less wiggles in the heating rate errors.
To examine the performance in more detail, the following plot evaluates fluxes and heating rates in each of the 13 CKDMIP longwave bands. The performance is strikingly better than in the equivalent plot for the ecRad-RRTMG simulations.
The following plot compares the instantaneous radiative forcing (change to net flux) at top-of-atmosphere and the surface, from perturbing the concentrations of individual well-mixed greenhouse gases from their present-day values, found by averaging over the 50 profiles of the Evaluation-1 dataset. For the minimum and maximum concentrations, the change to mean atmospheric heating rate is also evaluated. In this case we see that RRTMGP represents the radiative forcing of all gases well, and is much better than RRTMG at representing low concentrations of methane.
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