8 A Polarimetric Analysis of Ice Microphysical Processes in Snow, using Quasi-Vertial Profiles

Monday, 28 August 2017
Zurich DEFG (Swissotel Chicago)
Erica M. Griffin, CIMMS/Univ. of Oklahoma and NOAA/NSSL, Norman, OK

This study implements a new QVP methodology to investigate the microphysical evolution and significance of intriguing winter polarimetric signatures and their statistical correlations. QVPs of transitional stratiform and pure snow precipitation are analyzed using WSR-88D S-band data, alongside their corresponding environmental thermodynamic HRRR model analyses. QVPs of KDP and ZDR are implemented to demonstrate their value in interpreting elevated ice processes. Several fascinating and repetitive signatures are observed in the ZDR and KDP QVPs, in the DGL and at the tops of clouds. The most striking feature is maximum ZDR (up to 6 dB) in the DGL occurring near the -10 dBZ ZH contour within low KDP and during shallower and warmer cloud tops. Conversely, maximum KDP (up to 0.3° km-1) in the DGL occurs within low ZDR and during taller and colder cloud tops. Essentially, ZDR and KDP in the DGL are anti-correlated and strongly depend on cloud top temperature. Analyses also show correlations indicating larger ZDR within lower ZH in the DGL, and larger KDP within greater ZH in the DGL. The high ZDR regions are likely dominated by growth of a mixture of highly oblate dendrites and/or hexagonal plates, or prolate needles. Regions of high KDP are expected to be overwhelmed with snow aggregates and crystals with irregular or nearly spherical shapes, seeded at cloud tops. Furthermore, QVP indications of hexagonal plate crystals within the DGL are verified using in-situ microphysical measurements, demonstrating the reliability of QVPs in evaluating ice microphysics in upper regions of winter clouds.
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