...
Naturally the models tend to become more accurate with increasing numbers of k terms and in terms of RMSE in fluxes there appears to be scope for further increasing accuracy by futher increasing the number of k terms. When comparing models using the narrow and wide band structure for the same number of k terms, the narrow-band models tend to have a larger flux bias but a lower upper-atmosphere heating-rate RMSE. The plots for the climate-wide-38 model are presented and discussed next.
Detailed evaluation of the climate-
...
wide-38 model
To illustrate the performance of ecCKD, the plots are shown for one of the better shortwave CKD models it produced, targeting the climate application with the wide band structure and 38 k terms. The parts of the spectrum contributing to each k term are illustrated below. ecCKD automatically selects k terms with the aim of each one having a roughly similar error in reproducing the fluxes and heating rates in the parts of the spectrum it represents. It can be seen here that in the first three wide bands the k terms have been selected similarly to the longwave according to the locations of the strongest and weakest absorption lines. In the fourth wide band where line absorption is very weak, five k terms are used stacked in order of increasing Rayleigh optical depth. In the final wide band the k terms are selected according to the strength of continuum absorption by ozone and molecular oxygen.
...