AGW Observer

Observations of anthropogenic global warming

Papers on carbon dioxide and water vapor overlap

Posted by Ari Jokimäki on October 19, 2011

This is a list of papers on the overlap of the the absorption bands of carbon dioxide and water vapor. See also my article on the history of this issue including additional references. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

An improved treatment of overlapping absorption bands based on the correlated k distribution model for thermal infrared radiative transfer calculations – Xu et al. (2009) “This paper discusses several schemes for handling gaseous overlapping bands in the context of the correlated k distribution model (CKD). Commonly used methods are generally based on certain spectral correlation assumptions; thus they are either less accurate or less efficient and rarely apply to all overlapping bands. We propose a new treatment, which we developed from the traditional absorber amount weighted scheme and improved for application to various bands. This approach is quite efficient for treating the gaseous mixture as if it were a “single gas.” Numerical experiments demonstrate that the new scheme achieves high accuracy with a fast operating speed. To validate the new scheme, we conducted spectrally integrated calculations and sensitivity experiments in the thermal infrared region. Compared to line-by-line integration results, errors in cooling rates were less than 0.2 K/day below 70 Km and rose to 1 K/day from above 70 Km up to 100 Km; flux differences did not exceed 0.8 W/m2 at any altitude. Changes in CO2 and H2O concentrations slightly influenced the accuracy of the results.” Guangyu Shi, Na Xu, Biao Wang, Tie Dai, Jianqi Zhao, Journal of Quantitative Spectroscopy and Radiative Transfer, Volume 110, Issue 8, May 2009, Pages 435-451, doi:10.1016/j.jqsrt.2009.01.008.

A Mechanism of Tropical Precipitation Change due to CO2 Increase – Sugi & Yoshimura (2004) “A recent GCM study indicates that a weakening of tropical circulation associated with a slight increase in tropical precipitation may occur when atmospheric CO2 is increased. To further understand the mechanism of atmospheric temperature and precipitation changes associated with the greenhouse gas increase, a numerical experiment was conducted using an atmospheric general circulation model to investigate the separate effects of CO2 increase and sea surface temperature (SST) increase. It has been shown that the effect of CO2 increase is a reduction of radiative cooling in the lower troposphere, leading to a reduction of tropical precipitation. When atmospheric CO2 concentration is doubled (quadrupled) without changing the SST, the tropical precipitation is reduced by about 3% (6%) in the model. The reduction of radiative cooling is a result of the overlap effect of the CO2 15-μm and water vapor absorption bands. On the other hand, the effect of SST increase is the increase in atmospheric temperature and water vapor, leading to increases in radiative cooling and tropical precipitation. When SST is uniformly raised 2°C without changing the atmospheric CO2 concentration, the tropical precipitation is increased by about 6%.” Sugi, Masato, Jun Yoshimura, 2004, J. Climate, 17, 238–243, doi: 10.1175/1520-0442(2004)0172.0.CO;2. [Full text]

An optimal approach to overlapping bands with correlated k distribution method and its application to radiative calculations – Zhang et al. (2003) “It is found that the possibly achieved higher accuracy cannot be obtained for all overlapping bands if only one scheme is used to treat them in atmospheric absorption calculations. The commonly used multiplication transmittance scheme is not acceptable when correlation existing in the practical absorption spectra becomes strong. Therefore an optimized scheme to obtain k distribution parameters for overlapping bands is developed in this paper based on the completely uncorrelated, perfectly correlated, and partly correlated schemes. Two partial correlation formulae are given in the paper. Calculations of radiative flux and atmospheric heating (or cooling) rate are validated in detail using a line-by-line model described in the paper for six model atmospheres. The optimized scheme developed here has an accuracy in longwave clear skies of 0.07 K d−1 in the entire troposphere and 0.35 K d−1 above the tropopause; the accuracy of upward, downward, and net fluxes is 0.76 W m−2 at all altitudes. In shortwave region, the absolute errors of the heating rate are less than 0.05 K d−1 in the troposphere and less than 0.25 K d−1 above the tropopause; net flux errors are less than 0.9 W m−2 at all altitudes. For an ensemble of 42 diverse atmospheres, the new scheme guarantees an average maximum error of longwave heating rate of 0.068 K d−1 in troposphere, 0.22 K d−1 above tropopause, and an accuracy of 1.1 W m−2 of radiative net flux for all the levels. For a case of doubled CO2 concentration, radiative forcing calculations have an accuracy of 0.04 W m−2.” Zhang, H., T. Nakajima, G. Shi, T. Suzuki, and R. Imasu (2003), J. Geophys. Res., 108(D20), 4641, doi:10.1029/2002JD003358.

Feedback effects of atmospheric CO2-induced warming – Adem & Garduño (1998) “Using a thermodynamic climate model, temperature and precipitation changes due to a doubling of atmospheric CO2 content, including the corresponding feedback temperature increases of water vapor, snow-ice, and cloudiness, are evaluated. The feedback factors of the thermodynamic model are similar to those of Hansen et al. (1984) and Schlesinger (1986). The feedback factor of all three mechanisms combined is 4.0. The results depend mainly on the content of water vapor in the CO2 band (12-19μ). The temperature increase due to a doubling of CO2 is 1.2° C when there is water vapor in the band, and 3.5° C when there is no water vapor. Therefore, a possible cause of the strong differences in the solutions obtained by different models is the discrepancy in the amount and distribution of water vapor in the atmosphere, and in the treatment of its effect in the CO2 band.” Julián Adem, René Garduño, Geofísica Internacional, 1998, Volume 37, Issue 2, pages 55-70. [Full text]

Earth’s Annual Global Mean Energy Budget – Kiehl & Trenberth (1997) A quote from the article: “It is also important to note that different gases can absorb radiation at the same wavelengths; this is called the overlap effect. … Of this 125 W m-2 clear sky greenhouse effect, we can ask, what is the relative contribution of each atmospheric absorber? A detailed answer to this question is complicated by the overlap among individual gaseous absorption features. We calculate the longwave radiative forcing of a given gas by sequentially removing atmospheric absorbers from the radiation model. We perform these calculations for clear and cloudy sky conditions to illustrate the role of clouds to a given absorber for the total radiative forcing. Table 3 lists the individual contribution of each absorber to the total clear sky radiative forcing.” Kiehl, J. T., Kevin E. Trenberth, 1997: Earth’s Annual Global Mean Energy Budget. Bull. Amer. Meteor. Soc., 78, 197–208, doi: 10.1175/1520-0477(1997)0782.0.CO;2. [Full text]

Uncertainties in Carbon Dioxide Radiative Forcing in Atmospheric General Circulation Models – Cess et al. (1993) A quote from the article: “Fig. 3. (A) Scatter plot of LW clear (clear sky) radiative forcing, as generated by the GCMs, with and without overlap of the C02 absorption bands by water vapor absorption.” R. D. Cess, M.-H. Zhang, G. L. Potter, H. W. Barker, R. A. Colman, D. A. Dazlich, A. D. Del Genio, M. Esch, J. R. Fraser, V. Galin, W. L. Gates, J. J. Hack, W. J. Ingram, J. T. Kiehl, A. A. Lacis, H. Le Treut, Z.-X. Li, X.-Z. Liang, J.-F. Mahfouf, B. J. McAvaney, V. P. Meleshko, J.-J. Morcrette, D. A. Randall, E. Roeckner, J.-F. Royer, A. P. Sokolov, P. V. Sporyshev, K. E. Taylor, W.-C. Wang and R. T. Wetherald, Science 19 November 1993: Vol. 262 no. 5137 pp. 1252-1255, DOI: 10.1126/science.262.5137.1252.

The Intercomparison of Radiation Codes Used in Climate Models: Long Wave Results – Ellingson et al. (1991) A quote from the article: “One of the more overlooked problems in atmospheric absorption is the simultaneous absorption by two or more constituents across the same spectral interval (i.e., overlapping absorption). This is a particularly important problem for H2O and CO2 absorption in the 10- and 15-µm regions; … The issue of overlapping absorption is important to climate assessment particularly when one or both of the overlapping bands have strong absorption lines as is the case between the 15-µm bands of CO2 and the rotational band of H20 in the 12-18 µ m spectral region. Kiehl and Ramanathan [1982] studied the effect of this overlap on the radiative heating resulting from increased CO2, and they showed that there is a substantial reduction in the magnitude of increase in downward flux to the surface when the overlap is included. The greatest difference occurs at tropical H20 latitudes where there is a larger amount of H20. When the overlap with the continuum in the 12-18 µ m region is added, there is very little increase in downward flux to the surface in the tropics from doubled CO2 because the lower tropical atmosphere is already essentially opaque. When band overlap is included, there is a substantial increase in the tropospheric heating rates, which tends to compensate for the reduction in downward flux at the surface. Thus the degree of overlap in this spectral region affects the way the net warming is partitioned between the surface and the troposphere, but has only a weak effect on the total heating of the troposphere.” Ellingson, R. G., J. Ellis, and S. Fels (1991), J. Geophys. Res., 96(D5), 8929–8953, doi:10.1029/90JD01450. [Full text]

Overlapping effect of atmospheric H2O, CO2 and O3 on the CO2 radiative effect – Wang & Ryan (1983)“The effect of overlapping of atmospheric H2O, CO2 and O3 absorption bands on the radiation budget perturbation caused by CO2 doubling is investigated. Since the effect depends on the amount of gases in the atmosphere as well as on the strength of the absorption bands, we examine the effect associated with the variation of gas abundance using a narrow band representation for the absorption bands. This band representation allows for the absorption band structure and thus accounts for the correlation of the spectral feature of the absorbing gases. It is found that the presence of H2O and O3 has a relatively small influence on the CO2-induced perturbation of both solar and thermal radiation in the stratosphere. However, in troposphere and surface, the overlapping effect appears to be quite significant and changes the vertical distribution of the CO2-induced radiation energy perturbation. For example, in the infrared, the effect is to reduce the effectiveness for CO2 to emit and in the mean time increases the tropospheric absorption of downward thermal flux from the stratosphere due to CO2 increase; the net effect of the overlapping of gases is to increase the tropospheric warming and decrease the surface warming caused by CO2 increase. It is also found that the overlapping effect exhibits strong seasonal and latitudinal variations due primarily to variations in atmospheric H2O.” Wei-Chyung Wang, P. Barry Ryan, Tellus B, Volume 35B, Issue 2, pages 81–91, April 1983.

Radiative Heating Due to Increased CO2: The Role of H2O Continuum Absorption in the 12–18 μm Region – Kiehl & Ramanathan (1982)“In the 12–18 μm spectral region, the CO2 bands are overlapped by the H2O pure rotational band and the H2O continuum band. The 12–18 μm H2O continuum absorption is neglected in most studies concerned with the climatic effects of increased CO2. In this study, we examine the role of H2O–CO2 overlap in detail. Specifically, the effect of the water vapor continuum in the 12–18 μm region on the radiative heating due to increased CO2 is investigated. It is found that although the longwave surface radiative heating due to increased CO2 is considerably reduced at low latitudes by H2O continuum absorption, where water vapor partial pressures are high, the radiative heating of the surface/troposphere system as a whole is minimally altered.” Kiehl, J. T., V. Ramanathan, 1982, J. Atmos. Sci., 39, 2923–2926, doi: 10.1175/1520-0469(1982)0392.0.CO;2. [Full text]

Spectral and total emissivity of water vapor and carbon dioxide – Leckner (1972) A quote from abstract: “Total emissivity charts, pressure and overlap corrections based on calculations with spectral data are presented.” B. Leckner, Combustion and Flame, Volume 19, Issue 1, August 1972, Pages 33-48, doi:10.1016/S0010-2180(72)80084-1.

Infrared Absorption by Overlapping Bands of Atmospheric Gases – Hoover et al. (1967) “The spectral transmission of carbon monoxide, nitrous oxide, and mixtures of the two has been studied in the 2200-cm-1 region, where overlapping absorption bands occur. With spectral slit widths sufficiently large to include several absorption lines, it was found that the observed spectral transmittance of a mixture is equal to the product of the transmittances of the components measured separately, provided that sufficient nitrogen is added to give the same total pressure for all samples. This result was also obtained for overlapping bands of nitrous oxide and methane in the 1300-cm-1 region. The present work confirms Burch’s earlier studies of overlapping bands of CO2 and water vapor. An investigation of the possible breakdown of the multiplicative property of transmission for narrow spectral slit widths was inconclusive.” D. E. Burch, J. N. Howard, and Dudley Williams, J. Opt. Soc. Am., Vol. 46, Issue 6, pp. 452-455 (1956), doi:10.1364/JOSA.46.000452.

Further Studies of Overlapping Absorption Bands – Tubbs et al. (1967) No abstract. D. E. Burch, J. N. Howard, and Dudley Williams, J. Opt. Soc. Am., Vol. 46, Issue 6, pp. 452-455 (1956), doi:10.1364/JOSA.46.000452.

Infrared Transmission of Synthetic Atmospheres. V. Absorption Laws for Overlapping Bands – Burch et al. (1956)“Although Lambert’s law Tv=ekvω presumably applies to the absorption of gases in the infrared, the experimentally observed transmission Tv′ cannot be expressed by a simple relation of this type. It is observed, however, that in regions where the atmospheric carbon dioxide and water vapor absorption bands overlap Tv′(CO2+H2O)= Tv′(CO2Tv′(H2O) provided the total pressure P is constant. It is found that the total absorption ƒ Avdv for a synthetic atmospheric sample containing water vapor, carbon dioxide, and nitrogen can be expressed as ƒ AvdV= ƒ Av(H2O)dv+εƒ Av(CO2)dv, where ƒ Av(H2O)dv and ƒ Av(CO2)dv are given by the empirical relations obtained in earlier studies in the present series and ε is a fraction, which can be expressed in terms of the total absorption by water vapor.” D. E. Burch, J. N. Howard, and Dudley Williams, J. Opt. Soc. Am., Vol. 46, Issue 6, pp. 452-455 (1956), doi:10.1364/JOSA.46.000452.

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