Some Considerations for the Use of High-Resolution Mobile Radar Data in Tornado Intensity Determination

Abstract

The increasing number of mobile Doppler radars used in field campaigns across the central United States has led to an increasing number of high-resolution radar datasets of strong tornadoes. There are more than a few instances in which the radar-measured radial velocities substantially exceed the estimated wind speeds associated with the enhanced Fujita (EF) scale rating assigned to a particular tornado. It is imperative, however, to understand what the radar data represent if one wants to compare radar observations to damagebased EF-scale estimates. A violent tornado observed by the rapid-scan, X-band, polarimetric mobile radar (RaXPol) on 31 May 2013 contained radar-relative radial velocities exceeding 135 m s 21 in rural areas essentially devoid of structures from which damage ratings can be made. This case, along with others, serves as an excellent example of some of the complications that arise when comparing radar-estimated velocities with the criteria established in the EF scale. In addition, it is shown that data from polarimetric radars should reduce the variance of radar-relative radial velocity estimates within the debris field compared to data from single-polarization radars. Polarimetric radars can also be used to retrieve differential velocity, large magnitudes of which are spatially associated with large spectrum widths inside the polarimetric tornado debris signature in several datasets of intense tornadoes sampled by RaXPol.

Dissipation Characteristics of Tornadic Vortex Signatures Associated with Long-Duration Tornadoes

“…A pioneering advancement in tornado science occurred with the discovery of the tornadic vortex signature (TVS; Brown et al 1978), a bulk representation of a tornado that appears as a distinctive small-scale enhancement in azimuthal shear in Doppler radar data. Most tornadoes are not spatially well resolved by the radar, so a TVS is larger than the actual tornado (Brown et al 1978) and, owing to finite radar sampling, debris effects, and beam spreading, among other limitations, a TVS contains radial velocities that are less intense than wind speeds in the tornado near the surface (Snyder and Bluestein 2014). Nevertheless, the TVS serves as a useful proxy for the presence of a tornado in data from the Weather Surveillance Radar-1988 Doppler (WSR-88D) network.…”

“…Nevertheless, the TVS serves as a useful proxy for the presence of a tornado in data from the Weather Surveillance Radar-1988 Doppler (WSR-88D) network. In addition, the polarimetric tornadic debris signature (TDS; Ryzhkov et al 2005) is commonly associated with tornadoes to the point that tornado detection can be partially automated (Snyder and Ryzhkov 2015). Therefore, given a sufficiently short distance and clear line of sight between the radar and the tornado, identification of existing tornadoes in Doppler weather radar data is nearly ubiquitous.…”

Mobile Radar Observations of the Evolving Debris Field Compared with a Damage Survey of the Shawnee, Oklahoma, Tornado of 19 May 2013

“…structure of tornadoes such as suction vortices and improved definition of the low-level wind field (e.g., Wurman and Gill 2000;Bluestein et al 2004Bluestein et al , 2007aBluestein et al , 2015Bluestein et al , 2019Lee and Wurman 2005;Kosiba and Wurman 2010;Wakimoto et al 2011;Wurman and Kosiba 2013;Wurman et al 2013Wurman et al , 2014Kurdzo et al 2017). More recently, discrimination between hydrometeors and regions of lofted debris is possible with the addition of polarimetric measurements (e.g., Ryzhkov et al 2005;Bluestein et al 2007bBluestein et al , 2015Bluestein et al , 2019Kumjian and Ryzhkov 2008;Bodine et al 2013Bodine et al , 2014Snyder and Bluestein 2014;Kurdzo et al 2015;Tanamachi et al 2012;Wakimoto et al 2015Wakimoto et al , 2016Mahre et al 2018). The tornadic debris signature (TDS) was first proposed by Ryzhkov et al (2005) 1 to approximately delineate lofted debris based on high equivalent radar reflectivity factor, 2 low differential radar reflectivity (Z DR ), and low cross-correlation coefficient (r hv ) that are collocated with the tornadic rotational couplet observed in radial velocity.…”

Exploring the Feasibility of Using Commercially Available Vertically Pointing Wind Profiling Lidars to Acquire Thunderstorm Wind Profiles

“…Outside of fortuitous data collection, most of these observations will need to come from targeted field projects. Scanning mobile Doppler radars and radar profilers are frequently employed in severe thunderstorm field projects, but the quality and quantity of near-surface data is often limited by terrain, ground clutter, and scanning requirements in terms of scanning systems (Snyder and Bluestein, 2014). Typical profiling systems may not be subject to such issues, but radar profilers still have limited data availability near the surface and relatively poor spatial and temporal resolution.…”