Measurements from dual-polarization radars provide valuable insight into the microphysical processes within storms. A preliminary investigation of polarimetric observations during this event reveals several intriguing features, including a distinct localized downward excursion of the melting layer bright-band to the surface (characterized by reduced ρhv and locally maximized ZH and ZDR), an abundance of radial streaks of enhanced positive and negative ZDR due to depolarization of the transmitted radar signal, a flare echo or three-body scatter signature suggesting the presence of hailstones, and ZH as high as 60 dBZ in a region of thundersnow over Connecticut. Additionally, there were numerous signatures of enhanced ZDR located above the environmental freezing layer, which were associated with enhancements in KDP and slightly reduced ρhv. These enhanced ZDR values signified the presence of large, horizontally-oriented ice crystals in the subfreezing temperatures aloft, primarily due to lack of aggregation. The evolution of the aforementioned signatures are observed using data from the WSR-88D S-band polarimetric radar in Upton, NY (Long Island; KOKX) between 1100 UTC 8 February 2013 and 0300 UTC 9 February 2013.
This study investigates the origin and nature of these distinctive polarimetric signatures and the thermodynamic conditions within which they developed, using environmental thermodynamic data obtained from the experimental High-Resolution Rapid Refresh (HRRR) model. These data are used to interpret the polarimetric signatures of different types of ice crystal habits (e.g., needles, plates, stellars, and dendrites), which form in regimes of differing temperature and ice supersaturation. Additionally, polarimetric signatures at the surface are analyzed alongside observations of meteorological Phenomena Identification Near the Ground (mPING) surface data for verification of radar-indicated winter precipitation types.
Currently, the microphysical properties of winter storms have largely been unexplored, as polarimetric investigations have been focused on warm-season and severe convective storms. Yet, with the recent polarimetric upgrades to the United States WSR-88D network, ample dual-polarization data are now available for locations throughout the country, allowing for abundant observations of the microphysical properties of winter precipitation. The results of this study will further understanding of the fundamental microphysical processes within winter storms, as well as aid in improvement of the representation of winter precipitation in numerical modeling.
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