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Impact of Cirrus Crystal Shape on Solar Spectral Irradiance: A Case Study for Subtropical CirrusProfiles of in situ measurements of ice crystal size distribution of subtropical cirrus were used to calculate solar spectral irradiances above and below the clouds. Spheres and nonspherical ice crystal habits (columns, hollows, plates, bullets, and aggregates) were assumed in the calculations. The simulation results were compared to irradiance measurements from the NASA Solar Spectral Flux Radiometer. The microphysical and radiation data were collected by three aircraft during CRYSTAL-FACE. Two cirrus cases (optical thickness of about 1 and 7) from two mission dates (26 and 23 July 2002) were investigated in detail. The measured downwelling and upwelling irradiance spectra above the cirrus could mostly be reproduced by the radiation model to within +/- 5-10% for most ice crystal habits. Below the cirrus the simulations disagreed with the measured irradiances due to surface albedo variability along the flight track, and nonoptimal colocation between the microphysical and irradiance measurements. The impact of shape characteristics of the crystals was important for the reflected irradiances above the optically thin cirrus, especially for small solar zenith angles, because in this case single-scattering dominated the solar radiation field. For the cirrus of moderate optical thickness the enhanced multiple scattering tended to diminish particular shape features caused by nonspherical single-scattering. Within the ice absorption bands the shape-related differences in the absorption characteristics of the individual nonspherical ice crystals were amplified if multiple scattering prevailed. Furthermore, it was found that below the cloud the shape sensitivity of the downwelling irradiance spectra is larger compared to the nonsphericity effects on reflected irradiances above the cirrus. Finally, it was shown that the calculated cirrus solar radiative forcing could vary by as much as 26% depending on the ice crystal habit.
Document ID
20070002783
Acquisition Source
Ames Research Center
Document Type
Reprint (Version printed in journal)
Authors
Wendisch, Manfred
(National Academy of Sciences - National Research Council Moffett Field, CA, United States)
Pilewskie, Peter
(NASA Ames Research Center Moffett Field, CA, United States)
Pommier, John
(Bay Area Environmental Research Inst. Sonoma , CA, United States)
Howard, Steve
(Bay Area Environmental Research Inst. Sonoma , CA, United States)
Yang, Ping
(Texas A&M Univ. College Station, TX, United States)
Heymsfield, Andrew J.
(National Center for Atmospheric Research Boulder, CO, United States)
Schmitt, Carl G.
(National Center for Atmospheric Research Boulder, CO, United States)
Baumgardner, Darrel
(Universidad Nacional Autonoma de Mexico Mexico City, Mexico)
Mayer, Barnhard
(Deutsche Forschungsanstalt fuer Luft- und Raumfahrt Oberpfaffenhofen, Germany)
Date Acquired
August 24, 2013
Publication Date
February 4, 2005
Publication Information
Publication: Journal of Geophysical Research
Volume: 110
ISSN: 0148-0227
Subject Category
Meteorology And Climatology
Report/Patent Number
Paper-2004JD005294
Funding Number(s)
CONTRACT_GRANT: NCC2-1391
Distribution Limits
Public
Copyright
Other

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