92 How Well do ZDR Arc Metrics Indicate Potential for Strong Low-Level Rotation in Supercells?

Tuesday, 23 October 2018
Stowe & Atrium rooms (Stoweflake Mountain Resort )
Matthew B. Wilson, Univ. of Nebraska, Lincoln, NE; and M. S. Van Den Broeke

Differential reflectivity (ZDR) arcs are one of the most prominent dual-polarization features of supercell storms, and a strong, well-defined ZDR arc is often cited as indicating potential for a supercell to develop strong low-level rotation and potentially become tornadic. Recent observational and theoretical work has posited that this is due to the correlation between environmental low-level shear and storm-relative helicity and the magnitude of size sorting by the storm-relative wind which creates the ZDR arc signature. However, relatively little formal observational work has been done to quantify the relationship between time trends in ZDR arc metrics and low-level rotation over supercell life cycles. In this study, time series of manually calculated ZDR arc areal extent for a large sample of supercells are compared to time series of rotational velocity and Gibson Ridge Analyst 2 normalized rotation to determine how well trends in ZDR arc extent foreshadow changes in low-level rotation magnitude. In addition, time series of maximum and mean ZDR values in the arc obtained from an automatic ZDR arc identification and tracking algorithm in Python developed for this project are compared to rotational velocity and normalized rotation time series to determine how changes in these ZDR arc metrics relate to low-level rotation potential.
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