Line-by-Line model for the calculation of infrared radiation fluxes and cooling rates in clear sky atmospheres

A line-by-line model for the purpose of proving the influence of the ab- sorption line parr.-eters and the performance of the spectral resoiution on evaluating radiative transfer has been developed for clear sky conditions in the infra¡ed. It has been found that for small spectral ranges a resolution scheme with grouping subintervals according to the distribution of lines in conjunction with numerical Gaussian quadrature of different orders which depend on the absorption line ranges, assures high accuracy. For la,rger spec- tral intervals a resolution scheme using constant subintervals with 0.01- cm-1 widths in conjunction with an eight point Gaussian quadrature gives sufrcient accuracy. The influence of overlapping of absorption bands has been examined and it has been found that for the demands of models using fast approximative algorithms only overlapping of simultaneously two bands in the IR has to be considered. However, the inclusion of the L4 p,m ozone band to the cor¡e- sponding overlapping bands of H2o and Coz improves the accu¡acy in the lower stratosphere considerably. The weak Co2 band at r0.4 p,m should be additionally included to the 9.6 pm ozorLe band and the water vapor continu- um range, ifdrastically enlarged carbon dioxide concentration are considered. Finali¡ the influence of the uncertainties of line para,meter values on radi- ation transfer has been considered. For the assumption of an elror of *. r0 % for a.ll line strenghts and hatfwidths an error margin of up to L0 To fot the cool- ing rates in the stratosphere and a maximum about 4 % in the troposphere has been found