LINE-BY-LINE CALCULATION OF ATMOSPHERIC FLUXES AND COOLING RATES .2. APPLICATION TO CARBON-DIOXIDE, OZONE, METHANE, NITROUS-OXIDE AND THE HALOCARBONS

A line-by-line model (LBLRTM) has been applied to the calculation of c learsky longwave fluxes and cooling rates for atmospheres including CO 2, O-3, CH4, N2O, CCl4, CFC-11, CFC-12, and CFC-22 in addition to wate r vapor. The present paper continues the approach developed in an earl ier article in which the radiative properties of atmospheres with wate r vapor alone were reported. Tropospheric water vapor continues to be of principal importance for the longwave region due to the spectral ex tent of its absorbing properties, while the absorption bands of other trace species have influence over limited spectral domains. The princi pal effects of adding carbon dioxide are to reduce the role of the wat er vapor in the lower troposphere and to provide 72% of the 13.0 K d(- 1) cooling rate at the stratopause. In general, the introduction of un iformly mixed trace species into atmospheres with significant amounts of water vapor has the effect of reducing the cooling associated with water vapor, providing an apparent net atmospheric heating. The radiat ive consequences of doubling carbon dioxide from the present level are consistent with these results. For the midlatitude summer atmosphere the heating associated with ozone that occurs from 500 to 20 mbar reac hes a maximum of 0.25 K d(-1) at 50 mbar and partially offsets the coo ling of 1.0 K d(-1) contributed by H2O and CO2 at this level. In the s tratosphere the 704 cm(-1) band of ozone, not included in many radiati on models, contributes 25% of the ozone cooling rate. Radiative effect s associated with anticipated 10-year constituent profile changes, 199 0-2000, are presented from both a spectral and spectrally integrated p erspective. The effect of the trace gases has been studied for three a tmospheres: tropical, midlatitude summer, and midlatitude winter. Usin g these results and making a reasonable approximation for the polar re gions, we obtain a value for the longwave flux at the top of the atmos phere of 265.5 W m(-2), in close agreement with the clear-sky Earth Ra diation Budget Experiment (ERBE) observations. This agreement provides strong support for the present approach as a reference method for the study of radiative effects resulting from changes in the distribution s of trace species on global radiative forcing. Many of the results fr om the spectral calculations reported here are archived at the Carbon Dioxide Information and Analysis Center for use by the community.