This page evaluates CKD models generated by the MSTRN11 tool against the CKDMIP "Evaluation-1" line-by-line dataset. So far only a shortwave model has been evaluated.

# Shortwave

The shortwave model evaluated uses 30 bands with a total of 103 g-points. 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 red line in the central column of panels quantifies the bias averaging over all five solar zenith angles, so should be considered as a daytime average (divide by two to get an approximate diurnal average). The shaded regions in these panels encompass 95% of the data.

The following figure evaluates fluxes and heating rates for the present-day scenario in six wavenumber ranges from the CKDMIP "narrow" band structure that most closely coincide with the 30 MSTRN bands:

The following shows the error in the CKD fluxes and heating rates, i.e. the CKD value minus the line-by-line reference calculation:

We see from the figures above that the upwelling fluxes are excellent and the tropospheric heating rates are good. There is an underestimate of the mesospheric heating rate, which the band results reveal to be due to missing absorption by CO2, which has strong bands at 4.3 and 2.8 microns. This is believed to be due to difficulties in allocating g-points / k-terms to the most strongly absorbing parts of the CO2 spectrum, which are very narrow so account for a very small fraction of the solar spectrum.

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. It has been found by averaging over the 50 profiles of the Evaluation-1 dataset, and averaging over the five solar zenith angles; therefore these forcings correspond to daytime only. The CFCs have a tiny shortwave effect so have been excluded. For the minimum and maximum concentrations, the change to mean atmospheric heating rate is also evaluated. We see that the radiative forcing from changes to CO2 and CH4 is very good, except perhaps for an underestimate of the forcing from 8x CO2 (purple diamond in panel a). The forcing by N2O is overestimated by a factor of 2, although the absolute shortwave forcing by this gas is very weak, and other CKD models struggle with shortwave N2O forcing. It can also be seen that MSTRN underestimates the change to upper-stratosphere and mesosphere heating rate associated with perturbations to all three of these gases, even when the forcing in terms of fluxes is accurate. This is related to the underestimate of absolute CO2 heating in the meosphere noted above.

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