A High Resolution Hydrometer Phase Classifier Based on Analysis of Cloud Radar Doppler Spectra. Page: 2 of 6
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A HIGH RESOLUTION HYDROMETEOR PHASE CLASSIFIER BASED
ON ANALYSIS OF CLOUD RADAR DOPPLER SPECTRA
Edward Luke' and Pavlos Kollias2
1. Brookhaven National Laboratory
2. McGill University1. INTRODUCTION
The lifecycle and radiative properties of
clouds are highly sensitive to the phase of
their hydrometeors (i.e., liquid or ice).
Knowledge of cloud phase is essential for
specifying the optical properties of clouds, or
else, large errors can be introduced in the
calculation of the cloud radiative fluxes.
Current parameterizations of cloud water
partition in liquid and ice based on
temperature are characterized by large
uncertainty (Curry et al., 1996; Hobbs and
Rangno, 1998; Intriery et al., 2002). This is
particularly important in high geographical
latitudes and temperature ranges where
both liquid droplets and ice crystal phases
can exist (mixed-phase cloud). The mixture
of phases has a large effect on cloud
radiative properties, and the
parameterization of mixed-phase clouds has
a large impact on climate simulations (e.g.,
Gregory and Morris, 1996). Furthermore, the
presence of both ice and liquid affects the
macroscopic properties of clouds, including
their propensity to precipitate.
Despite their importance, mixed-phase
clouds are severely understudied compared
to the arguably simpler single-phase clouds.
In-situ measurements in mixed-phase
clouds are hindered due to aircraft icing,
difficulties distinguishing hydrometeor
phase, and discrepancies in methods for
deriving physical quantities (Wendisch et al.
1996, Lawson et al. 2001). Satellite-based
retrievals of cloud phase in high latitudes are
often hindered by the highly reflecting ice-
covered ground and persistent temperature
inversions. From the ground, the retrieval of
mixed-phase cloud properties has been the
subject of extensive research over the past
Corresponding author address: Edward
Luke, Department of Atmospheric Sciences,
Brookhaven National Laboratory, Bldg.
490D Bell Ave., Upton NY 11973 email:
eluke@bnl.gov
Presented at the American Meteorological
Cairns, Australia, August 6-10, 2007.20 years using polarization lidars (e.g.,
Sassen et al. 1990), dual radar wavelengths
(e.g., Gosset and Sauvageot 1992; Sekelsky
and McIntosh, 1996), and recently radar
Doppler spectra (Shupe et al. 2004).
Millimeter-wavelength radars have
substantially improved our ability to observe
non-precipitating clouds (Kollias et al., 2007)
due to their excellent sensitivity that enables
the detection of thin cloud layers and their
ability to penetrate several non-precipitating
cloud layers. However, in mixed-phase
clouds conditions, the observed Doppler
moments are dominated by the highly
reflecting ice crystals and thus can not be
used to identify the cloud phase. This limits
our ability to identify the spatial distribution
of cloud phase and our ability to identify the
conditions under which mixed-phase clouds
form.
2. ARM CLOUD RADARS
The United States Department of Energy
Atmospheric Radiation Measurement (ARM,
www.arm.gov) program operates millimeter-
wavelength cloud radars (at 35- and 94-GHz
radar frequencies) in several climatologically
distinct regions. The digital signal
processors for these radars were recently
upgraded (completed in 2006). A
comprehensive evaluation of the
performance of the ARM millimeter-
wavelength cloud radars (Kollias et al.,
2005) lead to a new operational sampling
strategy and modes. The new sampling
strategy for the ARM profiling clouds radars
(Kollias et al., 2007) includes significant
improvement in temporal resolution (i.e.,
less than 1 s for dwell and 2 s for dwell plus
processing), wider Nyquist velocities,
operational de-aliasing of the recorded
spectra, removal of pulse compression while
sampling the boundary layer, and
continuous recording of 128 and 256-point
FFT Doppler spectra from the 35- and 94-
GHz Doppler cloud radars. The post-
processing of the recorded Doppler spectra
Society's 33rd Conference on Radar Meteorology,6A.2
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Luke,E. & Kollias, P. A High Resolution Hydrometer Phase Classifier Based on Analysis of Cloud Radar Doppler Spectra., article, August 6, 2007; United States. (https://digital.library.unt.edu/ark:/67531/metadc896175/m1/2/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.