Evaluating and improving the treatment of gases in radiation schemes: the Correlated K-Distribution Model Intercomparison Project (CKDMIP)

Abstract. Most radiation schemes in weather and climate models use the “correlated k distribution” (CKD) method to treat gas absorption, which approximates a broadband spectral integration by N pseudo-monochromatic calculations. Larger N means more accuracy and a wider range of gas concentrations can be simulated but at greater computational cost. Unfortunately, the tools to perform this efficiency–accuracy trade-off (e.g. to generate separate CKD models for applications such as short-range weather forecasting to climate modelling) are unavailable to the vast majority of users of radiation schemes. This paper describes the experimental protocol for the Correlated K-Distribution Model Intercomparison Project (CKDMIP), whose purpose is to use benchmark line-by-line calculations: (1) to evaluate the accuracy of existing CKD models, (2) to explore how accuracy varies with N for CKD models submitted by CKDMIP participants, (3) to understand how different choices in the way that CKD models are generated affect their accuracy for the same N, and (4) to generate freely available datasets and software facilitating the development of new gas-optics tools. The datasets consist of the high-resolution longwave and shortwave absorption spectra of nine gases for a range of atmospheric conditions, realistic and idealized. Thirty-four concentration scenarios for the well-mixed greenhouse gases are proposed to test CKD models from palaeo- to future-climate conditions. We demonstrate the strengths of the protocol in this paper by using it to evaluate the widely used Rapid Radiative Transfer Model for General Circulation Models (RRTMG).

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Evaluating and improving the treatment of gases in radiation schemes: the Correlated K-Distribution Model Intercomparison Project (CKDMIP)

10.5194/gmd-2020-99 ◽

2020 ◽

Author(s):

Robin J. Hogan ◽

Marco Matricardi

Keyword(s):

General Circulation ◽

Computational Cost ◽

General Circulation Models ◽

Gas Absorption ◽

Distribution Model ◽

Radiative Transfer Model ◽

Transfer Model ◽

Climate Modelling ◽

Model Intercomparison ◽

Intercomparison Project

Abstract. Most radiation schemes in weather and climate models use the 'correlated k-distribution' (CKD) method to treat gas absorption, which approximates a broadband spectral integration by N pseudo-monochromatic calculations. Larger N means more accuracy and a wider range of gas concentrations can be simulated, but at greater computational cost. Unfortunately, the tools to perform this efficiency-accuracy trade-off (e.g., to generate separate CKD models for applications such as short-range weather forecasting to climate modelling) are unavailable to the vast majority of users of radiation schemes. This paper describes the experimental protocol for the Correlated K-Distribution Model Intercomparison Project (CKDMIP), whose purpose is to use benchmark line-by-line calculations: (1) to evaluate the accuracy of existing CKD models, (2) to explore how accuracy varies with N for CKD models submitted by CKDMIP participants, (3) to understand how different choices in way that CKD models are generated affects their accuracy for the same N, and (4) to generate freely available datasets and software facilitating the development of new gas-optics tools. The datasets consist of the high-resolution longwave and shortwave absorption spectra of nine gases for a range of atmospheric conditions, realistic and idealized. Thirty-four concentration scenarios for the well-mixed greenhouse gases are proposed to test CKD models from palaeo- to future-climate conditions. We demonstrate the strengths of the protocol in this paper by using it to evaluate the widely-used Rapid Radiative Transfer Model for General Circulation Models (RRTMG).

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The Palaeoclimate and Terrestrial Exoplanet Radiative Transfer Model Intercomparison Project (PALAEOTRIP): experimental design and protocols

Geoscientific Model Development ◽

10.5194/gmd-10-3931-2017 ◽

2017 ◽

Vol 10 (11) ◽

pp. 3931-3940 ◽

Cited By ~ 1

Author(s):

Colin Goldblatt ◽

Lucas Kavanagh ◽

Maura Dewey

Keyword(s):

Radiative Transfer ◽

Ad Hoc ◽

Climate Science ◽

Radiative Transfer Model ◽

Transfer Model ◽

Climate Modelling ◽

Atmospheric Conditions ◽

Model Intercomparison ◽

Radiative Transfer Calculation ◽

Intercomparison Project

Abstract. Accurate radiative transfer calculation is fundamental to all climate modelling. For deep palaeoclimate, and increasingly terrestrial exoplanet climate science, this brings both the joy and the challenge of exotic atmospheric compositions. The challenge here is that most standard radiation codes for climate modelling have been developed for modern atmospheric conditions and may perform poorly away from these. The palaeoclimate or exoclimate modeller must either rely on these or use bespoke radiation codes, and in both cases rely on either blind faith or ad hoc testing of the code. In this paper, we describe the protocols for the Palaeoclimate and Terrestrial Exoplanet Radiative Transfer Model Intercomparison Project (PALAEOTRIP) to systematically address this. This will compare as many radiation codes used for palaeoclimate or exoplanets as possible, with the aim of identifying the ranges of far-from-modern atmospheric compositions in which the codes perform well. This paper describes the experimental protocol and invites community participation in the project through 2017–2018.

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The Palaeoclimate and Terrestrial Exoplanet Radiative Transfer Model Intercomparison Project (PALAEOTRIP): experimental design and protocols

10.5194/gmd-2017-24 ◽

2017 ◽

Author(s):

Colin Goldblatt ◽

Lucas Kavenagh

Keyword(s):

Radiative Transfer ◽

Ad Hoc ◽

Climate Science ◽

Radiative Transfer Model ◽

Transfer Model ◽

Climate Modelling ◽

Atmospheric Conditions ◽

Model Intercomparison ◽

Radiative Transfer Calculation ◽

Intercomparison Project

Abstract. Accurate radiative transfer calculation is fundamental to all climate modelling. For deep palaeoclimate, and increasingly terrestrial exoplanet climate science, this brings both the joy and the challenge of exotic atmospheric compositions. The challenge here is that most standard radiation codes for climate modelling have been developed for modern atmospheric conditions, and may perform poorly away from these. The palaeoclimate or exoclimate modeller must either rely on these or use bespoke radiation codes, and in both cases rely on either blind faith or ad hoc testing of the code. In this paper, we describe the protocols for the Palaeoclimate and Terrestrial Exoplanet Radiative Transfer Model Intercomparison Project (PALAEOTRIP) to systematically address this. This will compare as many radiation codes used for palaeoclimate or exoplanets as possible, with the aim to constrain the ranges of far-from-modern atmospheric compositions in which the codes perform well. This paper describes the experimental protocol and invites community participation in the project through 2017.

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Towards a better representation of the solar cycle in general circulation models

Atmospheric Chemistry and Physics ◽

10.5194/acp-7-5391-2007 ◽

2007 ◽

Vol 7 (20) ◽

pp. 5391-5400 ◽

Cited By ~ 59

Author(s):

K. M. Nissen ◽

K. Matthes ◽

U. Langematz ◽

B. Mayer

Keyword(s):

Solar Cycle ◽

Heating Rate ◽

General Circulation ◽

Temperature Response ◽

General Circulation Models ◽

Short Wave ◽

Radiative Transfer Model ◽

Transfer Model ◽

Heating Rates ◽

Radiation Scheme

Abstract. We introduce the improved Freie Universität Berlin (FUB) high-resolution radiation scheme FUBRad and compare it to the 4-band standard ECHAM5 SW radiation scheme of Fouquart and Bonnel (FB). Both schemes are validated against the detailed radiative transfer model libRadtran. FUBRad produces realistic heating rate variations during the solar cycle. The SW heating rate response with the FB scheme is about 20 times smaller than with FUBRad and cannot produce the observed temperature signal. A reduction of the spectral resolution to 6 bands for solar irradiance and ozone absorption cross sections leads to a degradation (reduction) of the solar SW heating rate signal by about 20%. The simulated temperature response agrees qualitatively well with observations in the summer upper stratosphere and mesosphere where irradiance variations dominate the signal. Comparison of the total short-wave heating rates under solar minimum conditions shows good agreement between FUBRad, FB and libRadtran up to the middle mesosphere (60–70 km) indicating that both parameterizations are well suited for climate integrations that do not take solar variability into account. The FUBRad scheme has been implemented as a sub-submodel of the Modular Earth Submodel System (MESSy).

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Variable resolution general circulation models: Stretched-grid model intercomparison project (SGMIP)

Journal of Geophysical Research Atmospheres ◽

10.1029/2005jd006520 ◽

2006 ◽

Vol 111 (D16) ◽

Cited By ~ 59

Author(s):

Michael Fox-Rabinovitz ◽

Jean Côté ◽

Bernard Dugas ◽

Michel Déqué ◽

John L. McGregor

Keyword(s):

General Circulation ◽

General Circulation Models ◽

Model Intercomparison ◽

Variable Resolution ◽

Grid Model ◽

Intercomparison Project

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The Tibetan Plateau Summer Monsoon in the CMIP5 Simulations

Journal of Climate ◽

10.1175/jcli-d-12-00685.1 ◽

2013 ◽

Vol 26 (19) ◽

pp. 7747-7766 ◽

Cited By ~ 29

Author(s):

Anmin Duan ◽

Jun Hu ◽

Zhixiang Xiao

Keyword(s):

Tibetan Plateau ◽

Summer Monsoon ◽

General Circulation ◽

General Circulation Models ◽

Surface Heat ◽

The Tibetan Plateau ◽

Model Intercomparison ◽

Intercomparison Project ◽

Asian Summer ◽

Heat Low

Abstract Temporal variability within the Tibetan Plateau summer monsoon (TPSM) is closely linked to both the East and South Asian summer monsoons over several time scales but has received much less attention than these other systems. In this study, extensive integrations under phase 5 of the Coupled Model Intercomparison Project (CMIP5) historical scenarios from 15 coupled general circulation models (CGCMs) and Atmospheric Model Intercomparison Project (AMIP) runs from eight atmospheric general circulation models (AGCMs) are used to evaluate the performance of these GCMs. Results indicate that all GCMs are able to simulate the climate mean TPSM circulation system. However, the large bias associated with precipitation intensity and patterns remains, despite the higher resolution and inclusion of the indirect effects of sulfate aerosol that have helped to improve the skill of the models to simulate the annual cycle of precipitation in both AGCMs and CGCMs. The interannual variability of the surface heat low and the Tibetan high in most of the AGCMs resembles the observation reasonably because of the prescribed forcing fields. However, only a few models were able to reproduce the observed seesaw pattern associated with the interannual variability of the TPSM and the East Asian summer monsoon (EASM). Regarding long-term trends, most models overestimated the amplitude of the tropospheric warming and the declining trend in the surface heat low between 1979 and 2005. In addition, the observed cooling trend in the upper troposphere and the decline of the Tibetan high were not reproduced by most models. Therefore, there is still significant scope for improving GCM simulations of regional climate change, especially in regions near extensive mountain ranges.

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Improvement of the Simulation of Cloud Longwave Scattering in Broadband Radiative Transfer Models

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-18-0014.1 ◽

2018 ◽

Vol 75 (7) ◽

pp. 2217-2233 ◽

Cited By ~ 7

Author(s):

Guanglin Tang ◽

Ping Yang ◽

George W. Kattawar ◽

Xianglei Huang ◽

Eli J. Mlawer ◽

...

Keyword(s):

Radiative Transfer ◽

Multiple Scattering ◽

General Circulation ◽

General Circulation Models ◽

Radiative Transfer Model ◽

Transfer Model ◽

Discrete Ordinate ◽

Wide Range ◽

Scaling Methods ◽

Computational Errors

Abstract Cloud longwave scattering is generally neglected in general circulation models (GCMs), but it plays a significant and highly uncertain role in the atmospheric energy budget as demonstrated in recent studies. To reduce the errors caused by neglecting cloud longwave scattering, two new radiance adjustment methods are developed that retain the computational efficiency of broadband radiative transfer simulations. In particular, two existing scaling methods and the two new adjustment methods are implemented in the Rapid Radiative Transfer Model (RRTM). The results are then compared with those based on the Discrete Ordinate Radiative Transfer model (DISORT) that explicitly accounts for multiple scattering by clouds. The two scaling methods are shown to improve the accuracy of radiative transfer simulations for optically thin clouds but not effectively for optically thick clouds. However, the adjustment methods reduce computational errors over a wide range, from optically thin to thick clouds. With the adjustment methods, the errors resulting from neglecting cloud longwave scattering are reduced to less than 2 W m−2 for the upward irradiance at the top of the atmosphere and less than 0.5 W m−2 for the surface downward irradiance. The adjustment schemes prove to be more accurate and efficient than a four-stream approximation that explicitly accounts for multiple scattering. The neglect of cloud longwave scattering results in an underestimate of the surface downward irradiance (cooling effect), but the errors are almost eliminated by the adjustment methods (warming effect).

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Bias-corrected climate projections for South Asia from Coupled Model Intercomparison Project-6

Scientific Data ◽

10.1038/s41597-020-00681-1 ◽

2020 ◽

Vol 7 (1) ◽

Author(s):

Vimal Mishra ◽

Udit Bhatia ◽

Amar Deep Tiwari

Keyword(s):

Climate Change ◽

Impact Assessment ◽

South Asia ◽

General Circulation ◽

Coupled Model ◽

General Circulation Models ◽

River Basins ◽

Climate Projections ◽

Model Intercomparison ◽

Intercomparison Project

Abstract Climate change is likely to pose enormous challenges for agriculture, water resources, infrastructure, and livelihood of millions of people living in South Asia. Here, we develop daily bias-corrected data of precipitation, maximum and minimum temperatures at 0.25° spatial resolution for South Asia (India, Pakistan, Bangladesh, Nepal, Bhutan, and Sri Lanka) and 18 river basins located in the Indian sub-continent. The bias-corrected dataset is developed using Empirical Quantile Mapping (EQM) for the historic (1951–2014) and projected (2015–2100) climate for the four scenarios (SSP126, SSP245, SSP370, SSP585) using output from 13 General Circulation Models (GCMs) from Coupled Model Intercomparison Project-6 (CMIP6). The bias-corrected dataset was evaluated against the observations for both mean and extremes of precipitation, maximum and minimum temperatures. Bias corrected projections from 13 CMIP6-GCMs project a warmer (3–5°C) and wetter (13–30%) climate in South Asia in the 21st century. The bias-corrected projections from CMIP6-GCMs can be used for climate change impact assessment in South Asia and hydrologic impact assessment in the sub-continental river basins.

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