Journal cover Journal topic
Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
Geosci. Model Dev., 10, 2525-2545, 2017
https://doi.org/10.5194/gmd-10-2525-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Development and technical paper
03 Jul 2017
A radiative transfer module for calculating photolysis rates and solar heating in climate models: Solar-J v7.5
Juno Hsu1, Michael J. Prather1, Philip Cameron-Smith2, Alex Veidenbaum3, and Alex Nicolau3 1Department of Earth System Science, University of California Irvine, Irvine, California, 92697, USA
2Lawrence Livermore National Laboratory, Livermore, California, 94551, USA
3Department of Computer Science, University of California Irvine, Irvine, California, 92697, USA
Abstract. Solar-J is a comprehensive radiative transfer model for the solar spectrum that addresses the needs of both solar heating and photochemistry in Earth system models. Solar-J is a spectral extension of Cloud-J, a standard in many chemical models that calculates photolysis rates in the 0.18–0.8 µm region. The Cloud-J core consists of an eight-stream scattering, plane-parallel radiative transfer solver with corrections for sphericity. Cloud-J uses cloud quadrature to accurately average over correlated cloud layers. It uses the scattering phase function of aerosols and clouds expanded to eighth order and thus avoids isotropic-equivalent approximations prevalent in most solar heating codes. The spectral extension from 0.8 to 12 µm enables calculation of both scattered and absorbed sunlight and thus aerosol direct radiative effects and heating rates throughout the Earth's atmosphere.

The Solar-J extension adopts the correlated-k gas absorption bins, primarily water vapor, from the shortwave Rapid Radiative Transfer Model for general circulation model (GCM) applications (RRTMG-SW). Solar-J successfully matches RRTMG-SW's tropospheric heating profile in a clear-sky, aerosol-free, tropical atmosphere. We compare both codes in cloudy atmospheres with a liquid-water stratus cloud and an ice-crystal cirrus cloud. For the stratus cloud, both models use the same physical properties, and we find a systematic low bias of about 3 % in planetary albedo across all solar zenith angles caused by RRTMG-SW's two-stream scattering. Discrepancies with the cirrus cloud using any of RRTMG-SW's three different parameterizations are as large as about 20–40 % depending on the solar zenith angles and occur throughout the atmosphere.

Effectively, Solar-J has combined the best components of RRTMG-SW and Cloud-J to build a high-fidelity module for the scattering and absorption of sunlight in the Earth's atmosphere, for which the three major components – wavelength integration, scattering, and averaging over cloud fields – all have comparably small errors. More accurate solutions with Solar-J come with increased computational costs, about 5 times that of RRTMG-SW for a single atmosphere. There are options for reduced costs or computational acceleration that would bring costs down while maintaining improved fidelity and balanced errors.


Citation: Hsu, J., Prather, M. J., Cameron-Smith, P., Veidenbaum, A., and Nicolau, A.: A radiative transfer module for calculating photolysis rates and solar heating in climate models: Solar-J v7.5, Geosci. Model Dev., 10, 2525-2545, https://doi.org/10.5194/gmd-10-2525-2017, 2017.
Publications Copernicus
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Short summary
Solar-J is a high-fidelity solar radiative transfer Fortran 90 code. It has been developed for consistently calculating both the photolysis rates of important chemical species and the heating rates of the atmosphere and the Earth's surface. Its spectral range spans from 177 nm to 12 microns. It can be easily dropped in as a module in global climate–chemistry models.
Solar-J is a high-fidelity solar radiative transfer Fortran 90 code. It has been developed for...
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