Thursday, 10 November 2016
Broadway Rooms (Hilton Portland )
Ongoing hydrometeor size sorting in severe convective storms is revealed in polarimetric radar analyses by a separation of specific differential phase (KDP) and differential reflectivity (ZDR) enhancement regions. The magnitude of this separation distance and its orientation with respect to storm motion are thought to be linked to storm-relative helicity, and thus may provide information about a storm’s tornadic potential. Whereas previous studies have examined this separation qualitatively, herein we present a technique to quantify this ZDR- KDP separation. Within a specified area of interest (“analysis box”), the centroid of all precipitation data points (thresholded with co-polar correlation coefficient ρhv) exceeding a given value is found for both KDP and ZDR. From these KDP and ZDR centroids, the separation distance and orientation (“separation vector”) is computed. The sensitivity of the calculated separation vector and its trend leading up to tornadogenesis to varying the KDP and ZDR thresholds is tested. Further, we introduce an “adaptive threshold” that automatically chooses the highest threshold value for both KDP and ZDR for which there are a sufficient number of data points in that specific storm, allowing it to be applied generally to a variety of storms modes and environments.
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