The Near-surface Horizontal and Vertical Structure of Tornado Vortices as Revealed by High-Frequency Texas Tech Ka-band Mobile Doppler Radar Observations

The accurate characterization of the near-surface flow of tornadoes is paramount to the understanding of the damage they inflict, their maintenance mechanisms and, per recent theories (Lewellen and Lewellen 2007), possibly their genesis. Yet, for the importance, we have a staggering paucity of observations of actual tornado inflow. This observation is significantly hindered by how shallow the inflow region can be (from the surface to ~10-20 m AGL in the most extreme cases). As such, it is necessary to use radar observation platforms that are both mobile and transmit at high frequency, mitigating the effect of diffraction in inhibiting sufficiently narrow resolution to resolve the sub-structure of tornado vortices (i.e., high wavenumber structure) and keeping the Doppler velocity power spectrum free of contribution from ground targets.

During the Verification of the Origin of Rotation in Tornadoes Experiment in 2009 and 2010, and in subsequent opportunistic cases from 2011-2013, the Texas Tech Ka-band (TTUKa) radars were deployed to collect observations of tornado structure. Certain cases (e.g., Northwest Oklahoma - April 2012, Rozel, KS – May 2013) will be chosen for presentation. Specific points of emphasis will include: 1) the azimuthal axisymmetric profile of tangential and radial velocity within tornado vortices, 2) the resolved character and depth of the tornado inflow layer, and 3) the presence of horizontal circulations, secondaries in the radial plane of the tornado, and those in the near-tornado environment (e.g., along storm-scale boundaries).