Diagnosed Three-Dimensional Axisymmetric Structure of the Mulhall Tornado on 3 May 1999

Abstract

On 3 May 1999, an unusually large tornado that caused F4-level damage and killed several people was intercepted by the Doppler on Wheels (DOW) mobile radar near Mulhall, Oklahoma, from a range of 4 to 9 km, resulting in high-resolution volumetric data every 55 s up to 1.5-km altitude over a period of 14 min. For the first time, the evolution and three-dimensional structure of a tornado were deduced using the ground-based velocity track display (GBVTD) technique. After the circulation center was determined, the tangential wind and radial wind were derived from the GBVTD technique at each radius and height. In addition, the axisymmetric vertical velocity, angular momentum, vorticity, and perturbation pressure were deduced from the tangential and radial wind fields. This study focuses on the axisymmetric aspects of this tornado.The primary circulation of the Mulhall tornado consisted of an 84 m s Ϫ1 peak axisymmetric tangential wind with the radius of maximum wind (RMW) ranging from 500 to 1000 m. The secondary circulation exhibited a two-cell structure characterized by a central downdraft surrounded by an annular updraft near the RMW. The calculated maximum pressure deficit from a 3-km radius to the tornado center at 50-m altitude was Ϫ80 hPa. The maximum vorticity during the first 8 min of observation was located inside the RMW away from the tornado center. This vorticity profile satisfied the necessary condition of barotropic instability. As the tornado weakened afterward, the vorticity monotonically increased toward the center. The computed swirl ratios were between 2 and 6, consistent with the observed multiple vortex radar signatures and the vorticity pattern. Swirl ratios were generally smaller during the weakening phase.

Super High-Resolution Simulation of the 6 May 2012 Tsukuba Supercell Tornado: Near-Surface Structure and Its Evolution

“…The multiple-vortex tornado is characterized by several subvortices, which are associated with strong horizontal convergence and strong updraft near the surface. These features are consistent with the results of previous laboratory experiments (Ward 1972;Church et al 1979), idealized numerical simulation (e.g., Rotunno 1979;Lewellen et al 1997), and observational studies (Wurman 2002;Lee and Wurman 2005). Although horizontal winds are locally intensified by the subvortices, the strongest wind of the tornado occurs at the stage of shrinking of the vortex radius just prior to a transition to a multiple-vortex structure.…”

“…Thus, the simulated tornado evolved from a one-cell to a two-cell structure, and subsequently exhibited a multiple-vortex structure. Such a transition of the vortex structure was also observed in previous laboratory experiments (Ward 1972;Church et al 1979), idealized simulations using LES (e.g., Rotunno 1979;Lewellen et al 1997), and observational studies (e.g., Wurman 2002, Lee and Wurman 2005, Wurman et al 2014). The multiple-vortex structure was most distinct at about 26 m height and became obscure above 200 m height.…”

“…(1) are controllable and S is easily computed in the laboratory studies, it is difficult to calculate S for a tornado having an asymmetric structure in a realistic environment (Lee and Wurman 2005). In this study, we tried to calculate S, assuming an axisymmetric structure of the tornado vortex.…”

Low-Level Winds in Tornadoes and Potential Catastrophic Tornado Impacts in Urban Areas

“…The sign and radial profile of V. depends on whether the tornado vortex exhibits single-or two-celled structure (Fiedler and Rotunno 1986;Lewellen et al 1997). Observations of V. in actual tornadoes vary (Wurman et al 1996;Wurman and Gill 2000;Alexander and Wurman 2005;Lee and Wurman 2005), and the conditions that result in the differing structures are not known; therefore, V. is set to 0 m s _1 in these tornado simulations.…”

LIDAR ground-based velocity track display analyses and surface observations of a vortex shedding event observed at the Hong Kong International Airport on April 11, 2011

“…8, 9). Following a similar approach to that of Lee and Wurman (2005), Kosiba et al (2008Kosiba et al ( , 2014, Wurman (2010, 2013) and Wurman et al (2013) integration of surface weather buoys data with GBVTD wind retrievals derived from LIDAR data provided a time history of the three-dimensional wind fields of three vortices shedding from the mountain.…”