147 Causes and Implications of the Negative Lightning Jump Prior to the 31 March 2016 EF-2 Tornado during VORTEX-SE

Thursday, 10 November 2016
Broadway Rooms (Hilton Portland )
Austin D. Vacek, University of Alabama, Huntsville, AL; and S. M. Stough, L. D. Carey, and B. L. Medina

The VORTEX-SE (Verification of the Origins of Rotation in Tornadoes Experiment-Southeast) field project was conducted 01 March to 01 May, 2016 in southeastern United States to understand atmospheric factors and processes that influence the formation, structure, and intensity of tornadoes in order to advance prediction of tornadic storms. The Advanced Radar for Meteorological and Operational Research (ARMOR) C-band polarimetric and Doppler radar, UAH Mobile Alabama X-band (MAX) polarimetric and Doppler radar, two UAH 2nd generation Parsivel disdrometers, sounding systems, and the NASA MSFC Northern Alabama Lightning Mapping Array (NALMA) were utilized in 7 operational periods during VORTEX-SE. This study focuses on the kinematic, microphysical, and lightning properties of potential tornadic storms with an emphasis on total lightning flash rate trends influencing the intensity of convective updraft strength, and the thermodynamic relationship of hydrometeor properties on downdraft forcing affecting tornadogenesis.

On 31 March 2016 (IOP 3), a tornadic supercell evolved within the ARMOR and MAX southern dual-Doppler lobe producing an EF-2 tornado. The supercell possessed lightning flash rates less than 28 flashes minute-1 throughout its lifespan, but a lightning jump was observed 16 minutes prior to tornado formation. From previous studies, the presence of a lightning jump suggests the strengthening of the storm’s updraft speed and volume. However, a sudden decrease in lightning flash rates (or a “negative lightning jump”) occurred 8 minutes after the initial positive lightning jump.  Dual-Doppler radar analysis will be presented to show how updraft and downdraft characteristics evolve with respect to total lightning flash trends and dual-polarization signatures, including hydrometeor types and amounts. Relationships between storm kinematics, microphysics, lightning and tornadogenesis will be explored with a special emphasis on developing a better understanding of the causes and implications of the negative lightning jump.

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