the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Computation of longwave radiative flux and vertical heating rate with 4A-Flux v1.0 as integral part of the radiative transfer code 4A/OP v1.5
- 1LMD/IPSL, École Polytechnique, Institut Polytechnique de Paris, ENS, PSL Research University, Sorbonne Université, CNRS, Palaiseau France
- 2FX CONSEIL, École Polytechnique, F 91128, Palaiseau Cedex, France
- 1LMD/IPSL, École Polytechnique, Institut Polytechnique de Paris, ENS, PSL Research University, Sorbonne Université, CNRS, Palaiseau France
- 2FX CONSEIL, École Polytechnique, F 91128, Palaiseau Cedex, France
Abstract. Based on advanced spectroscopic databases, line-by-line and layer-by-layer radiative transfer codes numerically solve the radiative transfer equation with a very high accuracy. Taking advantage of its pre-calculated optical depth look-up table, the fast and accurate radiative transfer model Automatized Atmospheric Absorption Atlas OPerational (4A/OP) calculates the transmission and radiance spectra for a user defined layered atmospheric model. Here we present a module, called 4A-Flux, developed and implemented into 4A/OP in order to include the calculation of the clear-sky longwave radiative flux profiles and heating rate profiles at a very high spectral resolution. Calculations are performed under the assumption of local thermodynamic equilibrium, plane-parallel atmosphere and specular reflection on the surface. The computation takes advantage of pre-tabulated exponential integral functions that are used instead of a classic angular quadrature. Furthermore, the sublayer variation of the Planck function is implemented to better represent the emission of layers with a high optical depth. Thanks to the implementation of 4A-Flux, 4A/OP model have participated in the Radiative Forcing Model Intercomparison Project (RFMIP-IRF) along with other state-of-the-art radiative transfer models. 4A/OP hemispheric flux profiles are compared to other models over the 1800 representative atmospheric situations of RFMIP, yielding an Outgoing Longwave Radiation (OLR) mean difference between 4A/OP and other models of −0.148 W .m−2 and a mean standard deviation of 0.218 W .m−2, showing a good agreement between 4A/OP and other models. 4A/OP is applied to the Thermodynamic Initial Guess Retrieval (TIGR) atmospheric database to analyze the response of the OLR and vertical heating rate to several perturbations of temperature or gas concentration. This work shows that 4A/OP with 4A-Flux module can successfully be used to simulate accurate flux and heating rate profiles and provide useful sensitivity studies including sensitivities to minor trace gases such as HFC134a, HCFC22 and CFC113. We also highlight the interest for the modeling community to extend intercomparison between models to comparisons between spectroscopic databases and modelling to improve the confidence in model simulations.
Yoann Tellier et al.
Status: closed
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RC1: 'Comment on gmd-2021-325', Anonymous Referee #1, 21 Dec 2021
The paper describes an extension of the radiative transfer model Automatized Atmospheric Absorption Atlas OPerational (4A/OP). The original version of the model enables line-by-line simulations of radiances in the thermal spectral region. The extension 4A-Flux performs an angular integration of the radiances to obtain irradiances (fluxes) and heating rates, either vertically resolved or only at top of atmosphere (outgoing longwave radiation OLR). For the angular integration exponential integral functions are applied. The model has already participated in the Radiative Forcing Model Intercomparison Project (RFMIP) and performed well. As an application, OLR and heating rate profiles are calculated using the Thermodynamic Initial Guess Retrieval (TIGR) atmospheric database as model input.
The paper is generally well written and as a model description paper, it fits the scope of GMD, although it does not include substantial new concepts. I have some comments regarding the methodology which should be clarified before publication.General comments:
- There are several publications about the calculation of line-by-line irradiances (fluxes), heating rates etc. in the thermal region (e.g. Buehler et al. 2006 and references therein)
More scientific context including references to relevant publications should be included in the introduction.- The most commonly used methods to compute irradiances (fluxes) and heating rates are two-stream methods, which provide accurate results (e.g., Zdunkowski, W., Trautmann, T., & Bott, A. (2007). Radiation in the Atmosphere: A Course in Theoretical Meteorology. Cambridge: Cambridge University Press.). Please explain and justify why you used the exponential integral functions to perform the angular integration.
- The role of clouds and aerosols is not discussed. Can clouds/aerosols be handled by the 4A model? Can the model handle scattering at all? If not are there any plans to extend the model in this direction?
- Is specular reflection a good approximation for natural surfaces? I suppose Lambertian surface reflection is a much more realistic assumption. Please justify why you included specular reflection.
Minor comments:
l. 53: "The spectral integration was performed with either a Gaus-
sian quadrature or at a single angle under the diffuse approximation"-
I assume you mean angular integration?l. 107: "solution of the radiative transfer equation ..." -> here you may add that this solution is called Schwarzschild equation
Eq. 16: Please define g and c_p
Table 1: I did not understand why the computational time for the vertical profiles is so much higher, could you explain this? For the calculation of OLR you need to step through all layers. Couldn't you save the results at all layer boundaries to get the vertical flux profiles?
l. 387ff.: Which are the main processes responsible for the "kink"? Isn't this mainly due to absorption by the ozone layer? This would also explain why it appears at different altitudes for the different scenarios,
Fig. 7: (c1) and (f1) do not show heating rate difference but heating rate.
(c2) and (f2) show exactly the same as (b2) and (e2), the same scale on the x-axis.References:
Buehler, SA, A von Engeln, E Brocard, VO John, T Kuhn, and P Eriksson (2006), Recent developments in the line-by-line modeling of outgoing longwave radiation, JQSRT, 98(3), 446-457
Zdunkowski, W., Trautmann, T., & Bott, A. (2007). Radiation in the Atmosphere: A Course in Theoretical Meteorology. Cambridge: Cambridge University Press
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RC2: 'Comment on gmd-2021-325', Anonymous Referee #2, 04 Jan 2022
The comment was uploaded in the form of a supplement: https://gmd.copernicus.org/preprints/gmd-2021-325/gmd-2021-325-RC2-supplement.pdf
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AC1: 'Comment on gmd-2021-325', Yoann Tellier, 09 Apr 2022
All co-authors would like to express gratitude to both referees for providing insightful comments on the submitted manuscript. We have worked to provide the best answers to all comments and questions and to bring necessary corrections and improvements to the revised manuscript.
To read the final author comments on behalf of all co-authors, please refer to the supplement file named "final_author_response.pdf".
Status: closed
-
RC1: 'Comment on gmd-2021-325', Anonymous Referee #1, 21 Dec 2021
The paper describes an extension of the radiative transfer model Automatized Atmospheric Absorption Atlas OPerational (4A/OP). The original version of the model enables line-by-line simulations of radiances in the thermal spectral region. The extension 4A-Flux performs an angular integration of the radiances to obtain irradiances (fluxes) and heating rates, either vertically resolved or only at top of atmosphere (outgoing longwave radiation OLR). For the angular integration exponential integral functions are applied. The model has already participated in the Radiative Forcing Model Intercomparison Project (RFMIP) and performed well. As an application, OLR and heating rate profiles are calculated using the Thermodynamic Initial Guess Retrieval (TIGR) atmospheric database as model input.
The paper is generally well written and as a model description paper, it fits the scope of GMD, although it does not include substantial new concepts. I have some comments regarding the methodology which should be clarified before publication.General comments:
- There are several publications about the calculation of line-by-line irradiances (fluxes), heating rates etc. in the thermal region (e.g. Buehler et al. 2006 and references therein)
More scientific context including references to relevant publications should be included in the introduction.- The most commonly used methods to compute irradiances (fluxes) and heating rates are two-stream methods, which provide accurate results (e.g., Zdunkowski, W., Trautmann, T., & Bott, A. (2007). Radiation in the Atmosphere: A Course in Theoretical Meteorology. Cambridge: Cambridge University Press.). Please explain and justify why you used the exponential integral functions to perform the angular integration.
- The role of clouds and aerosols is not discussed. Can clouds/aerosols be handled by the 4A model? Can the model handle scattering at all? If not are there any plans to extend the model in this direction?
- Is specular reflection a good approximation for natural surfaces? I suppose Lambertian surface reflection is a much more realistic assumption. Please justify why you included specular reflection.
Minor comments:
l. 53: "The spectral integration was performed with either a Gaus-
sian quadrature or at a single angle under the diffuse approximation"-
I assume you mean angular integration?l. 107: "solution of the radiative transfer equation ..." -> here you may add that this solution is called Schwarzschild equation
Eq. 16: Please define g and c_p
Table 1: I did not understand why the computational time for the vertical profiles is so much higher, could you explain this? For the calculation of OLR you need to step through all layers. Couldn't you save the results at all layer boundaries to get the vertical flux profiles?
l. 387ff.: Which are the main processes responsible for the "kink"? Isn't this mainly due to absorption by the ozone layer? This would also explain why it appears at different altitudes for the different scenarios,
Fig. 7: (c1) and (f1) do not show heating rate difference but heating rate.
(c2) and (f2) show exactly the same as (b2) and (e2), the same scale on the x-axis.References:
Buehler, SA, A von Engeln, E Brocard, VO John, T Kuhn, and P Eriksson (2006), Recent developments in the line-by-line modeling of outgoing longwave radiation, JQSRT, 98(3), 446-457
Zdunkowski, W., Trautmann, T., & Bott, A. (2007). Radiation in the Atmosphere: A Course in Theoretical Meteorology. Cambridge: Cambridge University Press
-
RC2: 'Comment on gmd-2021-325', Anonymous Referee #2, 04 Jan 2022
The comment was uploaded in the form of a supplement: https://gmd.copernicus.org/preprints/gmd-2021-325/gmd-2021-325-RC2-supplement.pdf
-
AC1: 'Comment on gmd-2021-325', Yoann Tellier, 09 Apr 2022
All co-authors would like to express gratitude to both referees for providing insightful comments on the submitted manuscript. We have worked to provide the best answers to all comments and questions and to bring necessary corrections and improvements to the revised manuscript.
To read the final author comments on behalf of all co-authors, please refer to the supplement file named "final_author_response.pdf".
Yoann Tellier et al.
Model code and software
4A-Flux v1.0: the radiative flux and heating rate module integrated into 4A/OP v1.5 radiative transfer code Tellier, Y., Crevoisier, C., Armante, R., Dufresne, J.-L., and Meilhac, N. https://doi.org/10.5281/zenodo.5667737
Yoann Tellier et al.
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