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| Titel |
Cloud droplet size and liquid water path retrievals from zenith radiance measurements: examples from the Atmospheric Radiation Measurement Program and the Aerosol Robotic Network |
| VerfasserIn |
J. C. Chiu, A. Marshak, C.-H. Huang, T. Várnai, R. J. Hogan, D. M. Giles, B. N. Holben, E. J. O'Connor, Y. Knyazikhin, W. J. Wiscombe |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 21 ; Nr. 12, no. 21 (2012-11-06), S.10313-10329 |
| Datensatznummer |
250011568
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| Publikation (Nr.) |
 copernicus.org/acp-12-10313-2012.pdf |
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| Zusammenfassung |
| The ground-based Atmospheric Radiation Measurement Program (ARM) and NASA
Aerosol Robotic Network (AERONET) routinely monitor clouds using zenith
radiances at visible and near-infrared wavelengths. Using the transmittance
calculated from such measurements, we have developed a new retrieval method
for cloud effective droplet size and conducted extensive tests for
non-precipitating liquid water clouds. The underlying principle is to
combine a liquid-water-absorbing wavelength (i.e., 1640 nm) with a
non-water-absorbing wavelength for acquiring information on cloud droplet
size and optical depth. For simulated stratocumulus clouds with liquid water
path less than 300 g m−2 and horizontal resolution of 201 m, the
retrieval method underestimates the mean effective radius by 0.8 μm,
with a root-mean-squared error of 1.7 μm and a relative deviation of
13%. For actual observations with a liquid water path less than 450 g m−2 at the ARM Oklahoma site during 2007–2008, our 1.5-min-averaged
retrievals are generally larger by around 1 μm than those from combined
ground-based cloud radar and microwave radiometer at a 5-min temporal
resolution. We also compared our retrievals to those from combined shortwave
flux and microwave observations for relatively homogeneous clouds, showing
that the bias between these two retrieval sets is negligible, but the error
of 2.6 μm and the relative deviation of 22% are larger than those
found in our simulation case. Finally, the transmittance-based cloud
effective droplet radii agree to better than 11% with satellite
observations and have a negative bias of 1 μm. Overall, the retrieval
method provides reasonable cloud effective radius estimates, which can
enhance the cloud products of both ARM and AERONET. |
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