Insights into Tornado Structure Afforded by High-frequency Mobile Radar

Owing to the difficulty of obtaining direct measurements of tornadoes with sufficient spatial resolution, particularly in the vertical, much of our current understanding of low-level tornado substructure is derived from theory and simulation. While the latter approach affords a valuable four-dimensional depiction of the tornado vortex, observations are critical in corroborating these analyses, improving the design of future numerical experiments, and individually lending specific insights into the genesis, maintenance and dissipation mechanisms for tornadoes.

Since their construction in 2009, two Texas Tech Ka-band (TTUKa) radars have been tasked with the depiction of the low-level wind field within tornadoes. A portion of this work was carried out through the 2009 and 2010 field phases of the Verification of the Origin of Rotation in Tornadoes Experiment (VORTEX2). Though no significant tornadoes were observed during the VORTEX2 period, a number of weaker events were chronicled, including tornadoes on 18 May 2010 near Stinnett, TX and 13 June 2010 near Booker, TX. Since VORTEX2, the TTUKa radars have had three successful intercepts of more significant events, near Tipton, OK on 7 November 2011, Cherokee, OK on 14 April 2012 and Rozel, KS on 18 May 2013.

This presentation will highlight significant findings from these cases, with particular attention paid to the context of previous simulations of tornado structure. Some of these results corroborate that found by prior observational work. For instance, the azimuthal wind distribution is found to repeatedly better fit a Burgers-Rott rather than Rankine-Combined vortex profile. However, there is considerable variability in the outer flow across multiple cases that may have some bearing on the maintenance mechanisms tied to the radial transport of angular momentum. Particularly in regard to the vertical structure of these vortices, a number of insights will be offered, many of which have very limited observational precedent, including the structure of the corner flow region, asymmetries in the inflow boundary layer wind profile and the presence of significant ancillary regions of horizontal and vertical vorticity in proximity to the tornado. Many of these latter areas appear to be tied to storm-scale boundaries and descending reflectivity cores within the hook region.