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Cloud property estimates from zenith spectral measurements of scattered sunlight between 0.9 and 1.7 um

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Daniel, J. S. , Portmann, R. W. , Miller, H. , Solomon, S. , Langford, A. O. , Eubank, C. S. , Schofield, R. , Turner, D. D. and Shupe, M. D. (2006): Cloud property estimates from zenith spectral measurements of scattered sunlight between 0.9 and 1.7 um , Journal of Geophysical Research,111,D16208. . doi: 10.1029/2005JD006641
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Abstract:

A theoretical approach is used to quantify the information available to retrieve cloudphysical properties from data taken by a ground-based spectrometer measuring scatteredsunlight in the near-infrared wavelength region. Three wavelength regions between 0.9and 1.7 mm, each containing water vapor, liquid, and ice absorption features, are examinedusing a differential optical absorption spectroscopy optimal estimation retrieval technique.Cloud properties that can be retrieved include path-integrated liquid water path andpath-integrated ice water path (PLWP and PIWP), cloud liquid and ice temperatures, andthe second moment of the photon path distribution. The accuracy of these cloud propertyretrievals is estimated for a variety of simulated conditions, with key analysis assumptionsidentified. The sensitivity of the measurements in the longest wavelength region toliquid water and ice is high, allowing for accurate estimates of PLWP and PIWP underoptically thin clouds, while the shorter two wavelength bands provide more informationunder optically thicker clouds. Observations of mixed-phase clouds over Barrow, Alaska,are used to illustrate the practicality of the technique. Retrieved LWP values (inferredfrom PLWP) are compared to LWP estimates from a microwave radiometer and anatmospheric emitted radiance interferometer; PIWP estimates are compared to IWPestimates from a millimeter-wave cloud radar. Cloud liquid temperature and photon pathdistribution information retrieved from these data are also presented. Furthermore, wesuggest a technique for combining near-infrared spectral PLWP measurements withmicrowave radiometer observations to estimate cloud droplet effective radius.

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