Sunday, 10 August 2003: 9:15 AM
The Kellerville tornado during VORTEX: Damage survey and Doppler radar analyses
Unusual deviations or turns in tornado tracks, not associated with obvious changes in the parent stormís overall propagation, have been documented for a number of years. Unfortunately, there has been no comprehensive data set collected to date that has been able to verify or suggest hypotheses that would explain these deviations. A detailed aerial and ground survey of a long track (~50 km) F5 tornado that developed during VORTEX (Verification of the Origins of Rotations in Tornadoes Experiment) on June 8, 1995 will be presented. The survey revealed that the tornado exhibited unusual nonlinear movements at two different locations. One portion of the track was associated with a pronounced sinusoidal pattern while another location was characterized by a cusp-like pattern. For the first time, high-resolution dual-Doppler wind measurements can be used to evaluate mechanisms for such deviations from a linear tornado path. The analyses of data collected with ELDORA (Electra Doppler Radar) suggest that these departures are trochoidal marks (Note: a trochoid is a curve generated by a point on the radius of a circle as the circle rolls along a straight line) produced as the tornado was revolving within the larger-scale mesocyclone. The maximum vorticity associated with the mesocyclone at low levels were shown to be an unreliable indicator of the tornadoís intensity. Indeed, the F-scale damage assessment and the single-Doppler velocities suggested that the tornado was weakening at one location at the same time that the vertical vorticity associated with the low-level mesocyclone was increasing.
Vertical cross sections of wind, vertical vorticity, radar reflectivity, and perturbation pressure were photogrammetrically superimposed onto two pictures of the tornado. This merger of data provides a unique view of the structural relationship between the hook echo and the mesocyclone. One of the important conclusions was the lack of a definitive relationship between the widths and strengths of the mesocyclone and the tornado.