Publication Abstracts

Boucher et al. 1998

Boucher, O., S.E. Schwartz, T.P. Ackerman, T.L. Anderson, B. Bergstrom, B. Bonnel, P. Chylek, A. Dahlback, Y. Fouquart, Q. Fu, R.N. Halthore, J.M. Haywood, T. Iversen, S. Kato, S. Kinne, A. Kirkevåg, K.R. Knapp, A. Lacis, I. Laszlo, M.I. Mishchenko, S. Nemesure, V. Ramaswamy, D.L. Roberts, P. Russell, M.E. Schlesinger, G.L. Stephens, R. Wagener, M. Wang, J. Wong, and F. Yang, 1998: Intercomparison of models representing direct shortwave radiative forcing by sulfate aerosols. J. Geophys. Res., 103, 16979-16998, doi:10.1029/98JD00997.

The importance of aerosols as agents of climate change has recently been highlighted. However, the magnitude of aerosol forcing by scattering of shortwave radiation (direct forcing) is still very uncertain even for the relatively well characterized sulfate aerosol. A potential source of uncertainty is in the model representation of aerosol optical properties and aerosol influences on radiative transfer in the atmosphere. Although radiative transfer methods and codes have been compared in the past, these comparisons have not focused on aerosol forcing (change in net radiative flux at the top of the atmosphere). Here we report results of a project involving 12 groups using 15 models to examine radiative forcing by sulfate aerosol for a wide range of values of particle radius, aerosol optical depth, surface albedo, and solar zenith angle. Among the models that were employed were high and low spectral resolution models incorporating a variety of radiative transfer approximations as well as a line-by-line model. The normalized forcings (forcing per sulfate column burden) obtained with the several radiative transfer models were examined, and the discrepancies were characterized. All models simulate forcings of comparable amplitude and exhibit a milar dependence on input parameters. As expected for a non-light-absorbing aerosol, forcings were negative (cooling influence) except at high surface albedo combined with small solar zenith angle. The relative standard deviation of the zenith-angle-averaged normalized broadband forcing for 15 models was 8% for particle radius near the maximum in this forcing (∼0.2 µm) and at low surface albedo. Somewhat greater model-to-model discrepancies were exhibited at specific solar zenith angles. Still greater discrepancies were exhibited at small particle radii, and much greater discrepancies were exhibited at high surface albedos, at which the forcing changes sign; in these situations, however, the normalized forcing is quite small. Discrepancies among the models arise from inaccuracies in Mie calculations, differing treatment of the angular scattering phase function, differing wavelength and angular resolution, and differing treatment of multiple scattering. These results imply the need for standardized radiative transfer methods tailored to the direct aerosol forcing problem. However, the relatively small spread in these results suggests that the uncertainty in forcing arising from the treatment of radiative forcing of a well-characterized aerosol at well-specified surface albedo is smaller than some of the other sources of uncertainty in estimates of direct forcing by anthropogenic sulfate aerosols and anthropogenic aerosols generally.

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BibTeX Citation

  author={Boucher, O. and Schwartz, S. E. and Ackerman, T. P. and Anderson, T. L. and Bergstrom, B. and Bonnel, B. and Chylek, P. and Dahlback, A. and Fouquart, Y. and Fu, Q. and Halthore, R. N. and Haywood, J. M. and Iversen, T. and Kato, S. and Kinne, S. and Kirkevåg, A. and Knapp, K. R. and Lacis, A. and Laszlo, I. and Mishchenko, M. I. and Nemesure, S. and Ramaswamy, V. and Roberts, D. L. and Russell, P. and Schlesinger, M. E. and Stephens, G. L. and Wagener, R. and Wang, M. and Wong, J. and Yang, F.},
  title={Intercomparison of models representing direct shortwave radiative forcing by sulfate aerosols},
  journal={Journal of Geophysical Research},

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RIS Citation

ID  - bo02100q
AU  - Boucher, O.
AU  - Schwartz, S. E.
AU  - Ackerman, T. P.
AU  - Anderson, T. L.
AU  - Bergstrom, B.
AU  - Bonnel, B.
AU  - Chylek, P.
AU  - Dahlback, A.
AU  - Fouquart, Y.
AU  - Fu, Q.
AU  - Halthore, R. N.
AU  - Haywood, J. M.
AU  - Iversen, T.
AU  - Kato, S.
AU  - Kinne, S.
AU  - Kirkevåg, A.
AU  - Knapp, K. R.
AU  - Lacis, A.
AU  - Laszlo, I.
AU  - Mishchenko, M. I.
AU  - Nemesure, S.
AU  - Ramaswamy, V.
AU  - Roberts, D. L.
AU  - Russell, P.
AU  - Schlesinger, M. E.
AU  - Stephens, G. L.
AU  - Wagener, R.
AU  - Wang, M.
AU  - Wong, J.
AU  - Yang, F.
PY  - 1998
TI  - Intercomparison of models representing direct shortwave radiative forcing by sulfate aerosols
JA  - J. Geophys. Res.
JO  - Journal of Geophysical Research
VL  - 103
SP  - 16979
EP  - 16998
DO  - 10.1029/98JD00997
ER  -

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