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First radar echoes from cumulus cloudsIn attempting to use centimeter-wavelength radars to investigate the early stage of precipitation formation in clouds, 'mantle echoes' are rediscovered and shown to come mostly from scattering by small-scale variations in refractive index, a Bragg kind of scattering mechanism. This limits the usefulness of single-wavelength radar for studies of hydrometeor growth, according to data on summer cumulus clouds in North Dakota, Hawaii, and Florida, to values of reflectivity factor above about 10 dBZe with 10-cm radar, 0 dBZe with 5-cm radar, and -10 dBZe with 3-cm radar. These are limits at or above which the backscattered radar signal from the kinds of clouds observed can be assumed to be almost entirely from hydrometeors or (rarely) other particulate material such as insects. Dual-wavelength radar data can provide the desired information about hydrometeors at very low reflectivity levels if assumptions can be made about the inhomogeneities responsible for the Bragg scattering. The Bragg scattering signal itself probably will be a useful way to probe inhomogeneities one-half the radar wavelength in scale for studying cloud entrainment and mixing processes. However, this use is possible only before scattering from hydrometeors dominates the radar return.
Document ID
19930044825
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Knight, Charles A.
(NASA Headquarters Washington, DC United States)
Miller, L. J.
(NCAR Boulder, CO, United States)
Date Acquired
August 16, 2013
Publication Date
February 1, 1993
Publication Information
Publication: American Meteorological Society, Bulletin
Volume: 74
Issue: 2
ISSN: 0003-0007
Subject Category
Meteorology And Climatology
Accession Number
93A28822
Distribution Limits
Public
Copyright
Other

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