School of Meteorology (Defense)

Observations of Supercell Tornado Evolution using a Mobile, Rapid-Scan, X-band, Polarimetric Radar

Jana Houser

OU School of Meteorology

19 June 2013, 10:00 AM

National Weather Center, Room 5820
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

On 24 May, 2011, a severe weather outbreak spawned a series of strong to violent tornadoes across central Oklahoma. Data were collected from two of these tornadoes by a rapid-scanning, X-band, polarimetric mobile radar (RaXPol). The acquired dataset encompasses the intensification, mature and dissipation phases of an EF-3 tornado, and the genesis, intensification and mature phases of a subsequent EF-5 tornado. Volumetric observations over 360 degree PPIs at 9 elevation angles were collected on ~15 second time scales, and near-surface single elevation PPIs were collected every 2 seconds for a period of ~6 minutes during intensification of tornado 2. This study examines various aspects of the tornadoes’ evolutions in an attempt to address the following questions: 1) How does the rotation associated with the tornadic vortices evolve during tornadogenesis, intensification and decay? 2) How does the three-dimensional structure of the tornadoes change with time? 3) How are storm-scale features (such as gust fronts and downdrafts) involved with the decay and genesis processes? 4) How is the tornado debris signature evident in the polarimetric variables related to the wind field? and 5) What other features pertinent to tornado evolution can be observed from rapid-scan data? In order to answer these questions, single-Doppler analyses are performed that examine the evolution of rotation over all times and heights and that reconstruct the reflectivity, radial velocity, and cross-correlation coefficient parameters onto three-dimensional grids to examine the tornado structure and parameter interrelations. Additionally, a brief period of rapid-scan dual-Doppler coverage between RaXPol and the MWR-05XP enabled some storm-scale features to be resolved during the intensification of the second tornado, including the wind-field around a weak reflectivity band associated with a horizontal vortex that was viewed by the RaXPol crew.

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