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JOURNAL OF THE ATMOSPHERIC SCIENCES, 64, 2483-2501, 2007.
A Midlatitude Cirrus Cloud Climatology from the Facility for Atmospheric Remote
Sensing. Part V: Cloud Structural Properties.
K. Sassen, L. Wang, D. O'C. Starr, J. M. Comstock, and M. Quante
Abstract
In this fifth of a series of papers describing the extended-time high cloud observation program from the
University of Utah Facility for Atmospheric Remote Sensing, the structural properties of cirrus clouds over
Salt Lake City, Utah, are examined. Wavelet analysis is applied to a 10-yr record of cirrus cloud ruby (0.694 micron)
lidar backscatter data as a function of cloud height in order to study the presence of periodic cloud
structures, such as the signatures of Kelvin–Helmholtz instabilities, cirrus mammata, and uncinus cells (all
with length scales of 1–10 km), as well as mesoscale cloud organizations generally believed to be induced
by gravity waves. About 8.4% of the data display structures after passing a 95% confidence level test, but
an 80% confidence level, which seems better able to resolve structures spread over long periods, yields
16.4%. The amount of identified cloud structures does not change significantly with length scale from 0.2
to 200 km, although the frequency of mesoscale cloud structures tends to increase as length scales increase.
The middle-to-lower portion of cirrus clouds contains the most identified cloud structures, which seems
related to the mesoscale organization of fall streaks from cloud-top-generating cells. The variability of cirrus
cloud optical depth tau (defined by the standard deviation over mean tau) derived from a combined lidar and
infrared radiometer (LIRAD) analysis is shown to be largely independent of tau. Because visual examination
of the lidar displays also indicates that few cirrus layers can be considered horizontally homogeneous over
our typical 3-h lidar data collection period, the authors conclude that the clouds in their sample are
inherently inhomogeneous even though most cirrus structures are not revealed as periodic by wavelet
analysis.
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