Intercomparison of Radiation Codes in Climate Models (ICRCCM): Longwave Clear-Sky Results—A Workshop Summary

Luther, F. M.; Ellingson, Robert G.; Fouquart, Y.; Fels, Stephen B.; Scott, N. A.; Wiscombe, W. J.

doi:10.1175/1520-0477-69.1.40

Cited by 81 publications

(45 citation statements)

References 6 publications

(7 reference statements)

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“…A wide variety of radiative transfer models are currently in use, ranging from lineby-line models to broadband approaches. Intercomparison of results from these models show that the uncertainties in the radiative forcing for doubling of CO2 could be as large as 10% [Luther and Fouquart, 1984]. In this section we estimate the sensitivity of greenhouse gas radiative forcing to a number of the assumptions discussed above, including the use of the BBM versus the NBM, clear-sky versus cloudy sky forcing, instantaneous versus adjusted forcing, diffusivity factor-based versus angular integration-based forcings, and constant versus realistic profile-based forcings.…”

Section: Radiative Forcing Calculations Based On Single Global and Anmentioning

confidence: 99%

Radiative forcings and global warming potentials of 39 greenhouse gases

Jain¹,

Briegleb²,

Minschwaner³

et al. 2000

J. Geophys. Res.

133

181

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Abstract. The radiative forcings and global warming potentials for 39 greenhouse gases are evaluated using narrowband and broadband radiative transfer models. Unlike many previous studies, latitudinal and seasonal variations are considered explicitly, using distributions of major greenhouse gases from a combination of chemical-transport model results and Upper Atmosphere Research Satellite (UARS) measurements and cloud statistics from the International Satellite Cloud Climatology Project. The gases examined include CO2, CH4, N20, plus a number of chlorofiuorocarbons, hydrochlorofiuorocarbons, hydrofiuorocarbons, hydrochlorocarbons, bromocarbons, iodocarbons, and perfiuorocarbons (PFCs). The model calculations are performed on a 5 ø latitude grid from 82.5øS to 82.5øN. The radiative forcings determined by the model are then used to derive global warming potential for each of the compounds, which are compared with prior analyses. In addition, the latitudinal and seasonal dependence of radiative forcing since preindustrial time is calculated. The vertical profiles of the gases are found to be important in determining the radiative forcings; the use of height-independent vertical distributions of greenhouse gases, as used in many previous studies, produce errors of several percent in estimated radiative forcings for gases studied here; the errors for the short-lived compounds are relatively higher. Errors in evaluated radiative forcings caused by neglecting both the seasonal and the latitudinal distributions of greenhouse gases and atmospheres are generally smaller than those due to height-independent vertical distributions. Our total radiative forcing due to increase in major greenhouse gas concentrations for the period 1765-1992 is 2.32 Wm -2, only 2% higher than other recent estimates; however, the differences for individual gases are as large as 23%.

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Section: Radiative Forcing Calculations Based On Single Global and Anmentioning

confidence: 99%

Radiative forcings and global warming potentials of 39 greenhouse gases

Jain¹,

Briegleb²,

Minschwaner³

et al. 2000

J. Geophys. Res.

133

181

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“…The approach adopted for the numerical intercomparisons was similar to that used for the longwave cases that have already been reported by Luther et al [1988]: to start with simple cases, gradually increasing in complexity. The simplest cases correspond to purely absorbing atmospheres; molecular scattering and clouds or aerosols, added successively, increase the complexity of the radiative transfer problem.…”

Section: Introductionmentioning

confidence: 99%

Intercomparing shortwave radiation codes for climate studies

Fouquart¹,

Bonnel²,

Ramaswamy

1991

J. Geophys. Res.

178

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As a second step of the international program of Intercomparison of Radiation Codes Used inClimate Models (ICRCCM), an intercomparison of shortwave radiation models was initiated. Among the 26 codes that participated in the comparison were very detailed (line-by-line), narrow-band (high-spectral resolution), as well as highly parameterized (low-spectral resolution) models. A considerable spread was detected in the response of these models to a set of well-defined atmospheric profiles. Substantial discrepancies exist among models even for the simplest case of pure water vapor absorption with standard deviation ranging from 1% to 3% for the downward fluxes at the surface and from 6% to 11% for the total atmospheric absorption. The divergences in downward surface flux increase to nearly 4% when all absorbers and the molecular scattering are considered. In cloudy conditions the divergences range from 4% to 10%, depending on the cloud optical thickness. Another major uncertainty that has been identified is the spectral averaging of the scattering properties which can result in very significant errors for low spectral resolution codes. Since these errors appear to be systematic, they may induce unrealistic feedback mechanisms in numerical climate models. The amplitude of the differences between models is in many cases larger than the accuracy required for the achievements of several objectives of the World Climate Research Program. While reference solutions for the absorption and scattering in atmospheres can be obtained based on the state-of-the-art spectroscopic knowledge and rigorous computational techniques, the absolute tests of the validity of the radiation algorithms would be comprehensive field experiments in which the radiative and all relevant atmospheric parameters are measured to a high degree of accuracy. INTRODUCTIONRadiation is a primary process governing the general circulation of the atmosphere and is the basic means through which significant changes in the climate may occur. As such, its treatment in climate models requires careful attention. Instead, the idea that radiation is a science with a very well-established physical basis is widespread in the climate community. As a consequence, relatively little attention has been paid until recently to a careful calibration of the various hypotheses, simplifications, or parameterizations on which the radiation codes in climate models are based. It is widely Table 1) were selected and distributed among the community. A majority of the cases are for clear-sky conditions (i.e., no clouds). The test cases considered included clear-sky and overcast atmospheres. It was decided at the outset that intercomparisons between the various models for clear skies had to be analyzed and placed 8955

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“…The accuracy of present adding (see, WM0,1984or Luther et al, 1988 and in recent work of Tjemkes and Duynkerke (1990). The adding method presented in this work may be applied to these random-band models.…”

Section: Summary and Remarksmentioning

confidence: 53%

Some Developments of the Method to Apply Band Models to an Inhomogeneous Atmosphere

Aoki¹,

Shibata²

1990

Journal of the Meteorological Society of Japan

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An exact solution of the infrared radiative transfer through multi-homogeneous layers has been developed in the framework of a random band model for the Lorentz lines. Comparing with this solution the accuracy of the Curtis-Godson and Godson methods, which are currently used in calculating the radiative transfer through the inhomogeneous atmosphere, has been investigated. It has been shown that the error of the sequential procedure of Godson is variable depending on whether the transmittance is calculated upward or downward direction of the atmosphere. A new sequential procedure has been proposed using the analytical exact solution for two layers. It is shown that this new sequential procedure is of better accuracy than the methods of Curtis-Godson and Godson for the radiative transfer calculation of water vapor, carbon dioxide and ozone.

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Intercomparison of Radiation Codes in Climate Models (ICRCCM): Longwave Clear-Sky Results—A Workshop Summary

Cited by 81 publications

References 6 publications

Radiative forcings and global warming potentials of 39 greenhouse gases

Radiative forcings and global warming potentials of 39 greenhouse gases

Intercomparing shortwave radiation codes for climate studies

Some Developments of the Method to Apply Band Models to an Inhomogeneous Atmosphere

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