Physical interpretation of the spectral radiative signature in the transition zone between cloud-free and cloudy regions
Chiu, C., Marshak, A., Knyazikhin, Y., Pilewskie, P. and Wiscombe, W. J. (2009) Physical interpretation of the spectral radiative signature in the transition zone between cloud-free and cloudy regions. Atmospheric Chemistry and Physics, 9 (4). pp. 1419-1430. ISSN 1680-7324
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To link to this article DOI: 10.5194/acp-9-1419-2009
One-second-resolution zenith radiance measure- ments from the Atmospheric Radiation Measurement pro- gram’s new shortwave spectrometer (SWS) provide a unique opportunity to analyze the transition zone between cloudy and cloud-free air, which has considerable bearing on the aerosol indirect effect. In the transition zone, we find a re- markable linear relationship between the sum and difference of radiances at 870 and 1640 nm wavelengths. The intercept of the relationship is determined primarily by aerosol prop- erties, and the slope by cloud properties. We then show that this linearity can be predicted from simple theoretical con- siderations and furthermore that it supports the hypothesis of inhomogeneous mixing, whereby optical depth increases as a cloud is approached but the effective drop size remains un- changed.