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11 micrometer emissivities and droplet radii for marine stratocumulusThe results of a new multispectral infrared retrieval scheme for obtaining fractional cloud cover and 11 micrometer emissivity with those of the spatial coherence method which obtains fractional cloud cover assuming that the clouds are opaque at infrared wavelengths. Both methods are applied to 4-km NOAA advanced very high resolution radiometer global area coverage data for 250-km-scale regions containing single-layered marine stratocumulus off the coast of South America. The average 11 micrometer emissivity for low level clouds is found to be between 0.70 and 0.85. The low emissivity is evidently due to the thinning of clouds at their edges. Semitransparent cloud edges evidently make up a substantial portion of the area covered by such clouds. This result indicates that cloud cover obtained using the spatial coherence method is underestimated by 0.1 to 0.2, as has been claimed in a previous study. The fractional cloud cover for the ensemble of 250-km-scale regions studied here increased slightly from 0.60 for daytime observations to 0.63 for nighttime observations. The 11 micrometer emissivity also increased slightly, but about half of the increase was related to the increase in cloud cover and a decrease in the relative area covered by cloud edge material. Presumably, the other half was due to an increase in cloud liquid water. Cloud height showed no significant change. The average effective droplet radius increased from 9.3 micrometers for daytime observations to 10.2 micrometers at night.
Document ID
19950051603
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Luo, Gang
(Oregon State Univ. Corvallis, OR, United States)
Lin, Xijian
(Oregon State Univ. Corvallis, OR, United States)
Coakley, James A.
(Oregon State Univ. Corvallis, OR, United States)
Date Acquired
August 16, 2013
Publication Date
February 20, 1994
Publication Information
Publication: Journal of Geophysical Research
Volume: 99
Issue: D2
ISSN: 0148-0227
Subject Category
Meteorology And Climatology
Accession Number
95A83202
Funding Number(s)
CONTRACT_GRANT: NSF ATM-89-12669
Distribution Limits
Public
Copyright
Other

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