Transcript Presentation- A Simple Model for Cloud Radiative Transfer of West Atlantic Cumulus

A Simple Model for Cloud Radiative
Transfer of West Atlantic Cumulus
Chang Sun1, Jiaxi Wang2, Shuwan Huang2
1Scripps
Institution of Oceanography
2Department of Chemistry and Biochemistry
University of California, San Diego, 9500 Gilman Drive, La Jolla 92092, CA, United
States
Outline
•
•
•
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Background
Model
Results and Analysis
Conclusion
Clouds & Global Climate
Clouds & Earth’s Radiation Budget
Bull. Am. Met. Soc. 78, 197-208
Cumulus
 Piled clouds with a flat base and tops in the shape of a cauliflower
 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:
 Back scattering fraction (β) is zero
 Single scattering albedo wo is 0.95
 Zenith is 45°
DeVault J E el al., 1983
Model
• For longwave:
• a0 —— 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
• Depth of cloud: Z=ztop-zbase=1100 m
de Roode S R and Duynkerke P G., 1996
Formulas
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
0.25S0
• R & A increase
• T decreases
with concentration
• N>2N0, R barely increases,
nearly remains constant
Shortwave radiation
• Optical depth increases
linearly with
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 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！