Ground-Based Velocity Track Display (GBVTD) Analysis of W-Band Doppler Radar Data in a Tornado near Stockton, Kansas, on 15 May 1999

Abstract

On 15 May 1999, a storm intercept team from the University of Oklahoma collected high-resolution, W-band Doppler radar data in a tornado near Stockton, Kansas. Thirty-five sector scans were obtained over a period of approximately 10 min, capturing the tornado life cycle from just after tornadogenesis to the decay stage. A low-reflectivity “eye”—whose diameter fluctuated during the period of observation—was present in the reflectivity scans. A ground-based velocity track display (GBVTD) analysis of the W-band Doppler radar data of the Stockton tornado was conducted; results and interpretations are presented and discussed. It was found from the analysis that the axisymmetric component of the azimuthal wind profile of the tornado was suggestive of a Burgers–Rott vortex during the most intense phase of the life cycle of the tornado. The temporal evolution of the axisymmetric components of azimuthal and radial wind, as well as the wavenumber-1, -2, and -3 angular harmonics of the azimuthal wind, are also presented. A quasi-stationary wavenumber-2 feature of the azimuthal wind was analyzed from 25 of the 35 scans. It is shown, via simulated radar data collection in an idealized Burgers–Rott vortex, that this wavenumber-2 feature may be caused by the translational distortion of the vortex during the radar scans. From the GBVTD analysis, it can be seen that the maximum azimuthally averaged azimuthal wind speed increased while the radius of maximum wind (RMW) decreased slightly during the intensification phase of the Stockton tornado. In addition, the maximum azimuthally averaged azimuthal wind speed, the RMW, and the circulation about the vortex center all decreased simultaneously as the tornado decayed.

Doppler Velocity Signatures of Idealized Elliptical Vortices

“…Yamauchi et al (2002) used ground-based Doppler radar data to document a type of elliptical eyewall that remained nearly stationary, unlike the rotating cases of Olivia and Herb. A similar near-stationary elliptical reflectivity pattern has been observed in a tornado (Bluestein et al 2003a, b;Tanamachi et al 2006). Yamauchi et al (2002) hypothesized that this flow pattern can be generated by superimposing a deformation field on an axisymmetric vortex.…”

“…Their study also ruled out the possibility of aliasing due to tornado evolution during the fast scan time of ~6 s by their W-band mobile radar. However, it is possible that aliasing could occur in a fast moving and a small RMW (~80 m) tornado because of the vortex being considered stationary over the duration of the scan (Tanamachi et al 2006). It is also possible that another physical mechanism beyond those proposed in this study is responsible for the case study documented in Bluestein et al (2003b).…”

A New Parametric Model of Vortex Tangential-Wind Profiles: Development, Testing, and Verification

“…The model yields a smooth transition between solid-body rotation and potential flow in the annular zone of tangential velocity maximum. The azimuthally averaged tangential velocity profiles derived from W-band Doppler radar measurements Tanamachi et al 2007) at low altitudes resemble the Burgers-Rott profile. Because of constraints in the Burgers-Rott profile, the profile sometimes does not match some other Dopplerderived tangential wind profiles very well.…”

The Improvement to the Environmental Wind and Tropical Cyclone Circulation Retrievals with the Modified GBVTD (MGBVTD) Technique

“…The closeness of the individually retrieved axisymmetric winds at constant heights from KCRP and KBRO demonstrates the strength of the MGBVTD technique over the GBVTD technique and its potential to be included in real-time TC wind retrieval packages like VORTRAC and for research use. Note that GBVTD has been also successfully applied to retrieving tornado wind fields in recent years (Lee and Wurman 2005;Tanamachi et al 2007). It is recommended that MGBVTD be applied to tornado research in the future to investigate its performance compared to GBVTD for smaller-scale vortices as well.…”