A Polarimetric Analysis of Ice Microphysical Processes in Snow, Using Quasi-Vertical Profiles

摘要

This study implements a new quasi-vertical profile (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 High-Resolution Rapid Refresh model analyses. QVPs of K-DP and Z(DR) are implemented to demonstrate their value in interpreting elevated ice processes. Several fascinating and repetitive signatures are observed in the QVPs for differential reflectivity Z(DR) and specific differential phase K-DP, in the dendritic growth layer (DGL), and at the tops of clouds. The most striking feature is maximum Z(DR) (up to 6 dB) in the DGL occurring near the 210-dBZ Z(H) contour within low KDP and during shallower and warmer cloud tops. Conversely, maximum KDP (up to 0.3 degrees km (1)) in the DGL occurs within low Z(DR) and during taller and colder cloud tops. Essentially, Z(DR) and K-DP in the DGL are anti-correlated and strongly depend on cloud-top temperature. Analyses also show correlations indicating larger Z(DR) within lower Z(H) in the D-GL and larger K-DP within greater Z(H) in the DGL. The high-Z(DR) regions are likely dominated by growth of a mixture of highly oblate dendrites and/or hexagonal plates, or prolate needles. Regions of high K-DP 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 D-GL are verified using in situ microphysical measurements, demonstrating the reliability of QVPs in evaluating ice microphysics in upper regions of winter clouds.