Properties of semitransparent upper-level clouds deduced from multispectral imagery data Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3484zm319

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  • A multispectral retrieval method is developed on the 100 km regional scale to extract the temperature, particle size, fractional cover and 11-μm emissivity of clouds which may be semitransparent in the infrared based on emitted radiances. The scheme utilizes the nonlinear relationship between emitted radiances when clouds are semitransparent and form a single-layered system. The retrieval method has the limitation that the particle size must be sufficiently small that the extinction and absorption cross sections at the different wavelengths are significantly different. For combinations of emission at 11 and 12 μm, the droplets must have radii less than 20 μm for both ice and water; for 3.7 and 12 μm the droplets must have radii less than 60 μm for ice and less than 100 μm for water; for 3.7 and 8 μm the droplets must have radii less than l50 μm for both ice and water. The retrieval scheme together with the spatial coherence method is applied to the analysis of NOAA-11 4-km Advanced Very High Resolution Radiometer 3.7, 11 and 12-μm observations obtained during the First ISCCP Regional Experiment Intensive Field Observations, Kansas, 1991. The results indicate that clear skies, single-layered and multi-layered cloud systems constitute equal proportions of 100-km scale regions. For the upper-level, single-layered clouds, 100-km scale emissivity and fractional cloud cover are correlated and the average effective radius of ice particles in semitransparent clouds is about 10 μm. Numerical simulations are performed to determine the sensitivity of the retrieved results to errors in observations and model assumptions and to compare the results of the current algorithm to those obtained with a threshold algorithm like that used by ISCCP. For effective radii less than 15 μm, errors in the retrieved effective radius are less than 1.5 μm and errors in cloud temperature are less than 5 K. The fractional cloud cover may be underestimated by 0.15. The 11-μm emissivity may be overestimated by 0.30. For upper-level, semitransparent/broken clouds, the current algorithm is superior to the threshold algorithm in the determination of cloud temperature and effective radius.
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2012-04-11T15:21:43Z (GMT) No. of bitstreams: 1 LinXijian1996.pdf: 1879519 bytes, checksum: f74d86d5e55f925881ab095e892be1f2 (MD5)
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