Estimating Wind Speeds in Tornadoes Using Ground-based, Mobile/Portable Doppler Radars and a Doppler Lidar: A Review of Work Done by a Group from the University of Oklahoma, Norman (1987 - 2023)

A group consisting of graduate students and the author at the University of Oklahoma, Norman, has been probing tornadoes with mobile/portable Doppler radars since the late 1980s. Attempts were also made using a mobile Doppler lidar for several years. In this presentation, a summary of our efforts and milestones (Bluestein 2022) will be given.

The objectives of our field programs, conducted almost yearly, have been (1) to document tornadogenesis with the expectation of forming and testing hypotheses regarding the dynamics of tornadoes and (2) to map the horizontal and vertical variations of the wind field in tornadoes as near as possible to the ground and above. We first used a tripod-mounted, portable, X-band, CW/FM-CW, low-power, solid state radar with a wide beam (from LANL) to obtain Doppler spectra, from which the maximum wind speed could be estimated. It was found that the thermodynamic speed limit could be exceeded, as predicted by theory, and that F-5 winds speeds were measured for the first time at close range. A truck-mounted, scanning, pulsed, W-band Doppler radar (U Mass W-band) was then used to obtain extremely fine spatial resolution in a shallow volume, including vertical cross sections showing the variation with height of weak-echo holes/columns. A truck-mounted, scanning, pulsed, X-band radar (U Mass) was used simultaneously and later by itself to achieve lesser spatial resolution, but with greater volumetric coverage of the parent storm and to obtain data in a power for the first time, documenting debris signatures near the ground at close range. The most noteworthy datasets collected and analyzed were those of the Attica, Kansas tornado on 12 May 2004 and, with a polarimetric upgrade (U Mass X-Pol), the Greensburg, Kansas tornado on 4 May 2007. Subsequently, a hybrid, phased-array, rapid-scan, non-polarimetric, X-band, military Doppler radar (MWR-05XP) was used to document tornadogenesis from low to midlevels in supercells with high temporal, but less spatial resolution. The most significant dataset collected was that of the Goshen County, Wyoming tornado during VORTEX2 on 5 June 2009. Attempts were soon made using a pulsed-Doppler lidar system mounted on the same truck as the MWR-05XP, to document the wind field in tornadoes at ultra-high spatial resolution. Owing to intermittent problems with the lidar system and our inability to get within the effective clear-air range (~ 5 km) of tornadoes during time periods we used the lidar, data in tornadoes were not collected, but clear-air boundary-layer data were. Finally, a rapid-scan (mechanically scanning), truck- mounted, X-band, polarimetric, Doppler radar (RaXPol) was used to obtain documentation of the rapid evolution of cyclonic and anticyclonic tornadoes in supercells, especially in large tornadoes near El Reno, Oklahoma, on 24 May 2011 and 31 May 2013 and in weaker, but very-well documented tornadoes near Dodge City, Kansas in 2016 and Selden, Kansas in 2021. Multiple secondary vortices and satellite vortices were also documented. Ground-relative wind speeds as high as 135 m s^-1 (and possibly higher) were measured.

Based on our experiences over the years and current technology capabilities, we will suggest ways to improve further our radar measuring capabilities.

Reference:

Bluestein, H. B., 2022: Observations of tornadoes and their parent supercells using ground-based, mobile Doppler radars. Chapter 3, Remote Sensing of Water-Related Hazards (K. Zhang, Y. Hong and A. AghaKouchak, eds.), Geophys. Monogr., American Geophysical Union/Wiley, New York, 271, 31 – 67.