Multi-Radar Analysis of the 20 May 2013 Moore, Oklahoma Supercell through Tornadogenesis and Intensification

Clarice N Satrio,Charles M Kuster,David J Bodine,Robert D Palmer

doi:10.3390/atmos12030313

Abstract

A multi-radar analysis of the 20 May 2013 Moore, Oklahoma, U.S. supercell is presented using three Weather Surveillance Radars 1988 Doppler (WSR-88Ds) and PX-1000, a rapid-scan, polarimetric, X-band radar, with a focus on the period between 1930 and 2008 UTC, encompassing supercell maturation through rapid tornado intensification. Owing to the 20-s temporal resolution of PX-1000, a detailed radar analysis of the hook echo is performed on (1) the microphysical characteristics through a hydrometeor classification algorithm (HCA)—inter-compared between X- and S-band for performance evaluation—including a hail and debris class and (2) kinematic properties of the low-level mesocyclone (LLM) assessed through ΔVr analyses. Four transient intensifications in ΔVr prior to tornadogenesis are documented and found to be associated with two prevalent internal rear-flank downdraft (RFD) momentum surges, the latter surge coincident with tornadogenesis. The momentum surges are marked by a rapidly advancing reflectivity (ZH) gradient traversing around the LLM, descending reflectivity cores (DRCs), a drop in differential reflectivity (ZDR) due to the advection of smaller drops into the hook echo, a decrease in correlation coefficient (ρhv), and the detection of debris from the HCA. Additionally, volumetric analyses of ZDR and specific differential phase (KDP) signatures show general diffusivity of the ZDR arc even after tornadogenesis in contrast with explosive deepening of the KDP foot downshear of the updraft. Similarly, while the vertical extent of the ZDR and KDP columns decrease leading up to tornadogenesis, the phasing of these signatures are offset after tornadogenesis, with the ZDR column deepening the lagging of KDP.

Highlights

Characteristics of supercells and tornadoes are primarily analyzed through the use of radar observations and are greatly supplemented by the variety of sampling techniques utilized by each radar
While all other analyses and figure generation were done in Python. Conditions on this day were favorable for supercells and tornadoes, with convective initiation focused along an eastward bulge in the north-south oriented dryline in southwestern Oklahoma
The boundary may have provided enhanced pre-existing vorticity resulting in favorable conditions for tornadogenesis, which occurred at ∼1956 UTC [as concluded by National Weather Service

Summary

Introduction

Characteristics of supercells and tornadoes are primarily analyzed through the use of radar observations and are greatly supplemented by the variety of sampling techniques utilized by each radar. Other recent advancements have focused on improving spatial and temporal sampling—bridging the gap between finescale processes (e.g., supercell and tornado evolution) and relatively slower temporal sampling of WSR88Ds, whose timescales differ by 1–2 orders of magnitude—leading to the proliferation of mobile, rapid-scan, polarimetric radars in research (e.g., [1,2,3]). Such rapid-scan radars have the capability to observe the evolution of polarimetric signatures missed by operational radars, yet critical to understanding and predicting the formation and subsequent behavior of severe hazards. Rapid-scan radar systems are widely considered the future for meteorological research, owing to current limitations in temporal sampling capabilities [7]

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