A Simple Model for Cloud Radiative Transfer of

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A Simple Model for Cloud Radiative Transfer of West Atlantic Cumulus Chang Sun 1,

A Simple Model for Cloud Radiative Transfer of West Atlantic Cumulus Chang Sun 1, Jiaxi Wang 2, Shuwan Huang 2 1 Scripps Institution of Oceanography 2 Department of Chemistry and Biochemistry University of California, San Diego, 9500 Gilman Drive, La Jolla 92092, CA, United States

Outline • • Background Model Results and Analysis Conclusion

Outline • • Background Model Results and Analysis Conclusion

Clouds & Global Climate

Clouds & Global Climate

Clouds & Earth’s Radiation Budget Bull. Am. Met. Soc. 78, 197 -208

Clouds & Earth’s Radiation Budget Bull. Am. Met. Soc. 78, 197 -208

Cumulus Ø Piled clouds with a flat base and tops in the shape of

Cumulus Ø Piled clouds with a flat base and tops in the shape of a cauliflower Ø Typically in the boundary layer of atmosphere that is nearest to the surface of Earth. Roel Neggers, ISBN 90 -5808 -774 -3

Model • Target: West Atlantic Cumulus • For shortwave: Assumption: Ø Back scattering fraction

Model • Target: West Atlantic Cumulus • For shortwave: Assumption: Ø Back scattering fraction (β) is zero Ø Single scattering albedo wo is 0. 95 Ø Zenith is 45° De. Vault J E el al. , 1983

Model • For longwave: • a 0 —— mass absorption coefficient • W ——

Model • For longwave: • a 0 —— mass absorption coefficient • W —— liquid water path • Neglect the cloud reflectivity (Yamamoto et al. , 1970) G. L. Stephens, 1978

Western Atlantic Cumulus • r • n(r) Marile’ Colo’n-Robles et al. , 2006

Western Atlantic Cumulus • r • n(r) Marile’ Colo’n-Robles et al. , 2006

Western Atlantic Cumulus • Depth of cloud: Z=ztop-zbase=1100 m de Roode S R and

Western Atlantic Cumulus • Depth of cloud: Z=ztop-zbase=1100 m de Roode S R and Duynkerke P G. , 1996

Formulas

Formulas

Results N (# cm-3) total number concentration of drops 207. 1 wl (g /kg)

Results N (# cm-3) total number concentration of drops 207. 1 wl (g /kg) liquid water mixing ratio 0. 24 r (μm) mean drop size radius 6. 67 re (μm) drop equivalent radius 7. 52 σext (m-1) extinction cross section for shortwave radiation 0. 062 Wl (g m-2) liquid water path 339. 8 τext (m) optical depth for shortwave radiation 67. 80 T transmissivity for shortwave radiation 0. 28 R reflectivity for shortwave radiation 0. 55 A absorptivity for shortwave radiation 0. 16 ε emissivity for longwave ~1 Data of western Atlantic cumulus from Marile’ Colo’n-Robles et al. [2006]

Shortwave radiation • Incoming solar radiation 0. 25 S 0 • R & A

Shortwave radiation • Incoming solar radiation 0. 25 S 0 • R & A increase • T decreases with concentration • N>2 N 0, R barely increases, nearly remains constant

Shortwave radiation • Optical depth increases linearly with concentration

Shortwave radiation • Optical depth increases linearly with concentration

Longwave radiation • E has been near 1 at original concentration • When concentration

Longwave radiation • E has been near 1 at original concentration • When concentration increases, E gets closer to 1.

Conclusion • With droplets concentration rising, optical depth will increase linearly, which contributes to

Conclusion • With droplets concentration rising, optical depth will increase linearly, which contributes to more solar radiation reflection and longwave radiation emission of Western Atlantic cumulus. N↑----->τ↑-----> R, E↑ • Their ultimate effect on temperature of the earth is complex and remains to be explored

Thank you!

Thank you!