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

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-streammore » 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).« less

Authors:
 [1];  [1];  [2];  [3];  [4];  [5];  [6]
  1. Texas A & M Univ., College Station, TX (United States). Dept. of Atmospheric Sciences
  2. Texas A & M Univ., College Station, TX (United States). Dept. of Physics and Astronomy, and Inst. for Quantum Science and Engineering
  3. Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Climate and Space Sciences and Engineering
  4. Atmospheric and Environmental Research, Inc., Cambridge, MA (United States)
  5. Univ. of Wisconsin, Madison, WI (United States). Space Science and Engineering Center
  6. Texas A & M Univ., College Station, TX (United States). Dept. of Atmospheric Sciences; Univ. of Colorado, Boulder, CO (United States). Laboratory for Atmospheric and Space Physics
Publication Date:
Research Org.:
Univ. of Michigan, Ann Arbor, MI (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1454654
Alternate Identifier(s):
OSTI ID: 1541833
Grant/Contract Number:  
SC0012969
Resource Type:
Published Article
Journal Name:
Journal of the Atmospheric Sciences
Additional Journal Information:
Journal Volume: 75; Journal Issue: 7; Journal ID: ISSN 0022-4928
Publisher:
American Meteorological Society
Country of Publication:
United States
Language:
English
Subject:
Meteorology & Atmospheric Sciences

Citation Formats

Tang, Guanglin, Yang, Ping, Kattawar, George W., Huang, Xianglei, Mlawer, Eli J., Baum, Bryan A., and King, Michael D. Improvement of the Simulation of Cloud Longwave Scattering in Broadband Radiative Transfer Models. United States: N. p., 2018. Web. doi:10.1175/jas-d-18-0014.1.
Tang, Guanglin, Yang, Ping, Kattawar, George W., Huang, Xianglei, Mlawer, Eli J., Baum, Bryan A., & King, Michael D. Improvement of the Simulation of Cloud Longwave Scattering in Broadband Radiative Transfer Models. United States. doi:10.1175/jas-d-18-0014.1.
Tang, Guanglin, Yang, Ping, Kattawar, George W., Huang, Xianglei, Mlawer, Eli J., Baum, Bryan A., and King, Michael D. Mon . "Improvement of the Simulation of Cloud Longwave Scattering in Broadband Radiative Transfer Models". United States. doi:10.1175/jas-d-18-0014.1.
@article{osti_1454654,
title = {Improvement of the Simulation of Cloud Longwave Scattering in Broadband Radiative Transfer Models},
author = {Tang, Guanglin and Yang, Ping and Kattawar, George W. and Huang, Xianglei and Mlawer, Eli J. and Baum, Bryan A. and King, Michael D.},
abstractNote = {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).},
doi = {10.1175/jas-d-18-0014.1},
journal = {Journal of the Atmospheric Sciences},
number = 7,
volume = 75,
place = {United States},
year = {2018},
month = {6}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1175/jas-d-18-0014.1

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