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On the Nature and Extent of Optically Thin Marine low CloudsMacrophysical properties of optically thin marine low clouds over the nonpolar oceans (60 deg S-60 deg N) are measured using 2 years of full-resolution nighttime data from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). Optically thin clouds, defined as the subset of marine low clouds that do not fully attenuate the lidar signal, comprise almost half of the low clouds over the marine domain. Regionally, the fraction of low clouds that are optically thin (f(sub thin,cld)) exhibits a strong inverse relationship with the low-cloud cover, with maxima in the tropical trades (f(sub thin,cld) greater than 0.8) and minima in regions of persistent marine stratocumulus and in midlatitudes (f(sub thin,cld) less than 0.3). Domain-wide, a power law fit describes the cloud length distribution, with exponent beta = 2.03 +/- 0.06 (+/-95% confidence interval). On average, the fraction of a cloud that is optically thin decreases from approximately 1 for clouds smaller than 2 km to less than 0.3 for clouds larger than 30 km. This relationship is found to be independent of region, so that geographical variations in the cloud length distribution explain three quarters of the variance in f(sub thin,cld). Comparing collocated trade cumulus observations from CALIOP and the airborne High Spectral Resolution Lidar reveals that clouds with lengths smaller than are resolvable with CALIOP contribute approximately half of the low clouds in the region sampled. A bounded cascade model is constructed to match the observations from the trades. The model shows that the observed optically thin cloud behavior is consistent with a power law scaling of cloud optical depth and suggests that most optically thin clouds only partially fill the CALIOP footprint.
Document ID
Document Type
Reprint (Version printed in journal)
External Source(s)
Leahy, L. V.
(Washington Univ. Seattle, WA, United States)
Wood, R.
(Washington Univ. Seattle, WA, United States)
Charlson, R. J.
(Washington Univ. Seattle, WA, United States)
Hostetler, C. A.
(NASA Langley Research Center Hampton, VA, United States)
Rogers, R. R.
(NASA Langley Research Center Hampton, VA, United States)
Vaughan, M. A.
(NASA Langley Research Center Hampton, VA, United States)
Winker, D. M.
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
August 27, 2013
Publication Date
November 16, 2012
Publication Information
Publisher: American Geophysical Union
Subject Category
Meteorology And Climatology
Report/Patent Number
Funding Number(s)
WBS: WBS 653967.01.09.01
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