Infrared Radiation Parameterizations for the Minor CO2 Bands and for Several CFC Bands in the Window Region

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  • 1 Lockheed Engineering and Sciences Company, Hampton, Virginia
  • | 2 Laboratory for Atmospheres, NASA/Goddard Space Flight Center, Greenbelt, Maryland
  • | 3 Science Systems & Application, Inc., Lanham, Maryland
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Abstract

Fast and accurate parameterizations have been developed for the transmission functions of the CO2 9.4- and 10.4-μm bands, as well as the CFC-11, CFC-12, and CFC-22 bands located in the 8-12-μm region. The parameterizations are based on line-by-line calculations of transmission functions for the CO2 bands and on high spectral resolution laboratory measurements of the absorption coefficients for the CFC bands. Also developed are the parameterizations for the H2O transmission functions for the corresponding spectral bands. Compared to the high-resolution calculations, fluxes at the tropopause computed with the parameterizations are accurate to within 10% when overlapping of gas absorptions within a band is taken into account. For individual gas absorption, the accuracy is of order 0%–2%.

The climatic effects of these trace gases have been studied using a zonally averaged multilayer energy balance model, which includes seasonal cycles and a simplified deep ocean. With the trace gas abundances taken to follow the Intergovernmental Panel on Climate Change Low Emissions “B” scenario, the transient response of the surface temperature is simulated for the period 1900–2060. The minor CO2 and CFC bands contribute about 20%–25% of the total warming at the surface, which is comparable to the contribution from the CH4 and N2O bands. Collectively, these minor absorption bands account for 40%–45% of the total surface temperature increases. Thus, the climate warming due to absorption in these bands is comparable to that in the 15-μm CO2 band.

Abstract

Fast and accurate parameterizations have been developed for the transmission functions of the CO2 9.4- and 10.4-μm bands, as well as the CFC-11, CFC-12, and CFC-22 bands located in the 8-12-μm region. The parameterizations are based on line-by-line calculations of transmission functions for the CO2 bands and on high spectral resolution laboratory measurements of the absorption coefficients for the CFC bands. Also developed are the parameterizations for the H2O transmission functions for the corresponding spectral bands. Compared to the high-resolution calculations, fluxes at the tropopause computed with the parameterizations are accurate to within 10% when overlapping of gas absorptions within a band is taken into account. For individual gas absorption, the accuracy is of order 0%–2%.

The climatic effects of these trace gases have been studied using a zonally averaged multilayer energy balance model, which includes seasonal cycles and a simplified deep ocean. With the trace gas abundances taken to follow the Intergovernmental Panel on Climate Change Low Emissions “B” scenario, the transient response of the surface temperature is simulated for the period 1900–2060. The minor CO2 and CFC bands contribute about 20%–25% of the total warming at the surface, which is comparable to the contribution from the CH4 and N2O bands. Collectively, these minor absorption bands account for 40%–45% of the total surface temperature increases. Thus, the climate warming due to absorption in these bands is comparable to that in the 15-μm CO2 band.

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