The unexplained solar absorption and atmospheric H2O: a direct test using clear-sky data

Article English OPEN
Conant, William C. ; Vogelmann, Andrew M. ; Ramanathan, V. (2011)

This paper is motivated by several recent studies that have shown that observations of atmosphericsolar absorption systematically and significantly exceed model estimates. This papertests whether uncertainties in the physics of water vapor absorption in clear skies are directlyresponsible for this unexplained excess absorption. Radiative transfer calculations of clear-skysolar fluxes are compared to measurements in the tropical Pacific at the surface and the tropopause.We find that the atmospheric absorption in excess of that predicted by radiative transfermodels, if it exists, is less than the experimental uncertainty of 7 W m<sup>−2</sup> (diurnally averaged).Furthermore, the difference between observed and modeled absorption is essentially independentof water vapor amounts between 35 and 51 kg m<sup>−2</sup>. A more direct test of the accuracy ofmodeled water vapor absorption is conducted with two independent multi-spectral radiometersat the Atmospheric Radiation Measurement site in Oklahoma, each providing over 16 000surface measurements of direct solar radiation in the 0.94 mm region. These spectral data confirmstate-of-the-art radiation model computations of water vapor line absorption to within 5% forthe wavelength region tested. The model-observation agreement for both tropical andOklahoma data strongly suggests that uncertainties in the physics of water vapor absorptionin clear skies are not a source for any significant excess solar absorption, thus narrowing thesearch to other atmospheric constituents or water vapor in cloudy skies.DOI: 10.1034/j.1600-0870.1998.t01-1-00010.x
  • References (25)
    25 references, page 1 of 3

    Arking, A. 1996. Absorption of solar energy in the atmosphere. Discrepancy between model and observations. Science 273, 779-782.

    Blanchet, J.-P. and List, R. 1983. Estimation of optical properties of arctic haze using a numerical model. Atmosphere-Ocean 21, 444-465.

    Cess, R. D., Zhang, M. H., Minnis, P., Corsetti, L., Dutton, E. G., Forgan, B. W., Garber, D. P., Gates, W. L., Morcrette, J.-J., Potter, G. L., Ramanathan, V., Subasilar, B., Whitlock, C. H., Young, D. F. and Zhou, Y. 1995. Absorption of solar radiation by clouds: Observations Versus Models. Science 267, 496-499.

    Charlock, T. P. and Alberta, T. L. 1996. The CERES/ ARM/GEWEX Experiment (CAGEX) for the retrieval of radiative fluxes with satellite data. Bull. Am. Met. Soc. 77, 2673-2683.

    Chou, M.-D. and Zhao, W. 1997. Estimation and model validation of surface solar radiation and cloud radiative forcing using TOGA COARE measurements. J. Clim. 10, 610-620.

    Conant, W. C. 1996. An examination of the solar absorption under clear skies for the central equatorial Pacific. Observations versus models. MS thesis, University of California, 50 pp.

    Conant, W. C., Ramanathan, V., Valero, F. P. J. and Meywerk, J. 1997. An examination of the clear-sky solar absorption over the central equatorial pacific: observations versus models. J. Climate 10, 1874-1884.

    Harrison, L. C. and Michalsky, J. J. 1994. Objective algorithms for the retrieval of optical depths from ground-based measurements. Appl. Optics 33, 5126-5132.

    Harrison, L. C., Michalsky, J. J. and Berndt, J. 1994. Automated multifilter rotating shadow-band radiometer. An instrument for optical depth and radiation measurements. Appl. Optics 33, 5118-5125.

    Kiehl, J. T. and Trenberth, K. E. 1997. Earth's annual global mean energy budget. Bull. Am. Meteorol. Soc. 78, 197-208.

  • Metrics
    No metrics available
Share - Bookmark