Convective Meteorology (Mesoscale Dynamics)

Influences of Larger-Scale Vortex Variability on Tornado Pressure Minima in an Outer-Flow Region: Explorations Using a Parametric Tangential Wind Model

Bim Wood

Research Meteorologist
NOAA/OAR/National Severe Storms Laboratory

09 September 2016, 3:00 PM

National Weather Center, Room 5600
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

Previous studies have neglected to distinguish between a central pressure deficit due to a tornado itself and due to a mesocyclone in which the tornado is embedded. In order to obtain improved understanding of the influences of larger-scale vortex variability on smaller-scale tornado pressure deficits, a parametric tangential wind model supplemented with a cyclostrophic speed equation was used to explore the role that the variability plays in influencing radial pressure deficits by deducing radial pressure deficit distributions from radial profiles of hypothetically superpositioned, dual-maxima tangential velocities in the free atmosphere, where a dominant swirling flow was in approximate cyclostrophic balance. The cyclostrophic approximation was partitioned into two separate components, allowing one to scrutinize and determine which of the concentric vortices contributes most significantly to the tornado pressure minima. The model parametrically constructed a smaller-scale, stronger vortex (rapidly swirling flow) that was centered within a larger-scale, weaker vortex (slowly swirling flow) to represent a tornado centered within a supercell, low-level mesocyclone above a tornado boundary layer. The radial pressure deficit fluctuations were varied by changing one of five key velocity-controlling parameters assigned to one vortex to represent a variety of vortex strength. Based on eight experiments, the larger-scale, weaker (smaller-scale, stronger) vortex contributed less (more) to the total pressure deficit than the smaller-scale stronger (larger-scale, weaker) vortex. The stronger vortex centered within the larger-scale, weaker vortex has a larger central pressure minimum than it does in the absence of the larger-scale vortex.

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