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Intercomparison of shortwave radiative transfer codes and measurements
Remote Sensing Division, Naval Research Laboratory, Washington, D. C., USA
NASA New Millennium Program, Jet Propulsion Laboratory, Pasadena, California, USA
Atmospheric Sciences Division, Brookhaven National Laboratory, Upton, New York, USA
Solar and Thermal Atmospheric Radiation, NOAA Climate Monitoring and Diagnostics Laboratory, Boulder, Colorado, USA
Spectral Sciences Inc., Burlington, Massachusetts, USA
Laboratoire d'Optique Atmospherique, Villeneuve d'Ascq, France
Laboratoire d'Optique Atmospherique, Villeneuve d'Ascq, France
Earth System Science Interdisciplinary Center, University of Maryland at College Park, College Park, Maryland, USA
Laboratory for Atmospheres, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Department of Meteorology, Pennsylvania State University, University Park, Pennsylvania, USA
ELICO, Université du Littoral Côte d'Opale, Wimereux, France
Kurchatov Institute, Moscow, Russia
Laboratoire d'Optique Atmospherique, Villeneuve d'Ascq, France
NOAA Geophysical Fluid Dynamics Laboratory, Princeton University, Princeton, New Jersey, USA
Institute for Computational Earth System Science, University of California, Santa Barbara, California, USA
Center for Atmospheric Sciences, Hampton University, Hampton, Virginia, USA
NOAA National Environmental Satellite Data and Information Service, Camp Springs, Maryland, USA
Earth System Science Interdisciplinary Center, University of Maryland at College Park, College Park, Maryland, USA
Pacific Northwest National Laboratory, Richland, Washington, USA
Department of Atmospheric Sciences, Institute of Astronomy and Geophysics, University of Sao Paulo, Sao Paulo, Brazil
NOAA Geophysical Fluid Dynamics Laboratory, Princeton University, Princeton, New Jersey, USA
Institute for Computational Earth System Science, University of California, Santa Barbara, California, USA
Institute for Computational Earth System Science, University of California, Santa Barbara, California, USA
Canada Centre for Remote Sensing, Natural Resources Canada, Ottawa, Ontario, Canada
Climate and Radiation Branch, Laboratory for Atmospheres, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Computation of components of shortwave (SW) or solar irradiance in the surface-atmospheric system forms the basis of intercomparison between 16 radiative transfer models of varying spectral resolution ranging from line-by-line models to broadband and general circulation models. In order of increasing complexity the components are: direct solar irradiance at the surface, diffuse irradiance at the surface, diffuse upward flux at the surface, and diffuse upward flux at the top of the atmosphere. These components allow computation of the atmospheric absorptance. Four cases are considered from pure molecular atmospheres to atmospheres with aerosols and atmosphere with a simple uniform cloud. The molecular and aerosol cases allow comparison of aerosol forcing calculation among models. A cloud-free case with measured atmospheric and aerosol properties and measured shortwave radiation components provides an absolute basis for evaluating the models. For the aerosol-free and cloud-free dry atmospheres, models agree to within 1% (root mean square deviation as a percentage of mean) in broadband direct solar irradiance at surface; the agreement is relatively poor at 5% for a humid atmosphere. A comparison of atmospheric absorptance, computed from components of SW radiation, shows that agreement among models is understandably much worse at 3% and 10% for dry and humid atmospheres, respectively. Inclusion of aerosols generally makes the agreement among models worse than when no aerosols are present, with some exceptions. Modeled diffuse surface irradiance is higher than measurements for all models for the same model inputs. Inclusion of an optically thick low-cloud in a tropical atmosphere, a stringent test for multiple scattering calculations, produces, in general, better agreement among models for a low solar zenith angle (SZA = 30°) than for a high SZA (75°). All models show about a 30% increase in broadband absorptance for 30° SZA relative to the clear-sky case and almost no enhancement in absorptance for a higher SZA of 75°, possibly due to water vapor line saturation in the atmosphere above the cloud.
Received 28 July 2004; accepted 23 February 2005; published 3 June 2005.
Citation: (2005), Intercomparison of shortwave radiative transfer codes and measurements, J. Geophys. Res., 110, D11206, doi:10.1029/2004JD005293.
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