Observational Analysis of the Electrical and Kinematic Structure of a Tornadic Supercell

Vertical variability in graupel and ice mass distribution, when collated with LMA data like lightning initiation, channel propagation, flash source densities, and charge polarity, can provide insights into the formation and evolution of the tornadic storm as a whole. Recent studies have found that under similar environmental instability conditions, a storm can attain either normal or anomalous charge structure depending upon the mixed-phase microphysics. Environmental thermodynamics (lapse rate, mixing and entrainment) together with storm dynamics (updraft speeds, volume) influence the variability of the supercooled liquid water content (SCLW) within a storm. Thus, the storm dynamics partly controls the SCLW, which in turn controls the charge structure of the storm. It has also been established through previous studies that the differential reflectivity column height, measured by a polarimetric radar, can serve as an indicator of updraft strength. We aim to use high temporal resolution polarimetric radar data in combination with lightning mapping array data to investigate the fundamental relations between the kinematical, microphysical, and lightning properties of a tornadic supercell.

On 19 May 2013, the University of Oklahoma (OU) Advanced Radar Research Center’s mobile Rapid-scan, X-band, Polarimetric (RaXPol) radar scanned a tornado near Shawnee, Oklahoma which had a varying intensity throughout its lifecycle. At its most severe, the tornado produced EF-4 category winds. The radar was deployed three times, scanning the tornadic storm in PPI scan mode from a lowest tilt of 1° to 19° at an interval step of 2°, producing volume scans approximately every 40 s.

These radar observations are analyzed in conjunction with observations from the Oklahoma Lightning Mapping Array (OKLMA). The OKLMA detects lightning flash locations in three dimensions based on the time-of-arrival differences of very high frequency (VHF) emissions from discontinuous breakdown of lightning channels. Using estimates of mixed-phase ice mass through hydrometeor classification and vertical profiles of polarimetric variables, the SCLW content can be inferred. We present our preliminary findings regarding lightning behavior and SCLW in the Shawnee tornadic storm, with a particular emphasis on the period immediately preceding tornadogenesis.