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Transcript of 1 Do Polluted Clouds Have Sharper Cloud Edges? Christine Chiu, Julian Mann, Robin Hogan University...
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Do Polluted Clouds Have Sharper Cloud Edges?
Christine Chiu, Julian Mann, Robin Hogan University of Reading
Alexander Marshak, Warren WiscombeNASA Goddard Space Flight Center
Graham Feingold, Allison McComiskeyNOAA Earth System Research Laboratory
Importance of understanding aerosol-to-cumulus transition
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• Cumulus clouds increase heat and moisture transport from the surface to the free troposphere, and strongly influence atmospheric state variables and cloud cover.
• It remains challenging to model their transitions to stratocumulus or deep convection
• Cumulus clouds are also strongly affected by ambient aerosols
Clouds in more polluted air have sharper edges
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1liquid water path (g/m2)
• due to faster evaporation of the smaller cloud droplets
10 100 1000courtesy of G. Feingold
clean (100 cm-3)
0 km 6.4 km
6.4 kmpolluted (1000 cm-3)
0 km 6.4 km
6.4 km
Koran et al. (2009)
Our aim
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• To investigate whether observations support this finding that clouds in polluted environments have sharper cloud edges
Defining cloud edge width as the distance from clear sky to cloud optical depth of 2
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polluted
cloud optical depth 2 3
0 km 6.4 km
6.4 kmclean
0 km 6.4 km
6.4 km
0
100
200
300
400
Clean Polluted
Mean difference in cloud edge width between
clean and polluted cases is statistically significant
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cloud edge width (m)
mean=120mean=80
significant
0 100 200 300 400 50010
20
30
50
70
80
90
95
LES: 95% clouds have cloud edges within 200-m in the polluted case; 350-m in the clean case
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cumulative probability (%)
polluted clean
cloud edge width (m)
need high-resolution
measurements
2-channel Narrow-Field-Of-View radiometer:1-s, 1.2 FOV, 673 (RED) & 870 (NIR) nm
2NFOV
Measuring cloud edge width using cloud optical depth retrieved from 2NFOV
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Azores in 2009 and 2010
China in 2008
COPS in Germany, 2007
We focus on three AMF campaigns
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courtesy of ARM Climate Research Facility’s Photostream
We focus on low, non-precipitating clouds
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• Radar/lidar data – cloud base height < 2 km
• Microwave radiometer – liquid water path
• Aerosol observing system – aerosol light scattering
• Merged sounding – wind speed at cloud layers
• 2NFOV – clouds should be big enough and away from each other with an at least 20-sec time interval
thanks to people who involve and provide these data products
Seasonal distribution of Azores cases
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05
101520253035
6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12Month (2009-2010)
~ 200 cases
Cu
Sc
Sc+Cu
courtesy of Jasmine Rémillard, Pavlos Kollias
Compare cloud edge width statistics between simulations and observations
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Cloud edge width as a function of aerosol light scattering
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Range of cloud edge distance (m)
0
100
200
300
400
500
LES-clean polluted COPS-clean polluted Azores-clean polluted China-clean polluted
11080
12080
235
17085
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LES COPS Azores China
7300 5800 145 140 130 10 4 13
y-axis: Range of cloud edge width (m)observations: threshold in aerosol light scattering 50 Mm-1
significant not significant
0 100 200 300 400 50010
20
30
50
70
80
90
95
COPS: 95% clouds have cloud edges within250-m in polluted cases; 350-m in clean cases
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COPS
cumulative probability (%)
polluted
clean
cloud edge width (m)
LES
0 100 200 300 400 50010
20
30
50
70
80
90
95
LES
Azores: 95% clouds have cloud edges within 300-m in polluted cases; 450-m in clean cases
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Azores
cumulative probability (%)
polluted
clean
cloud edge width (m)
Azores
Summary
• Observations show that clouds in more polluted air have sharper cloud edges, but statistical significance is not always met
• The distribution of cloud edge width in simulations is similar to that observed in COPS, not Azores
• We plan to relax criteria of case selections to allow us to stratify cases based on meteorological factors
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