The Dodge City Tornadoes on 24 May 2016: Damage Survey, Photogrammetric Analysis Combined with Mobile Polarimetric Radar Data

Abstract

Polarimetric measurements recorded by a mobile X-band radar are combined with photographs of the Dodge City, Kansas, tornado to quantitatively document the evolving debris cloud. An inner annulus or tube of high radar reflectivity encircled the tornado at low levels. A column of low cross-correlation coefficient ρhv was centered on the funnel cloud during the early stage of the tornado’s life cycle. In addition, two areas of low ρhv were located near the inner annulus of high radar reflectivity and were hypothesized to be regions of high debris loading that have been reproduced in simulations of lofted debris. Another column of low ρhv was a result of strong wind speeds that were progressively lofting small debris and dust as inflow rotated around and within the weak echo notch of the hook echo. A column of negative differential reflectivity ZDR was also centered on the tornado and was hypothesized to result from common debris alignment. The polarimetric structure undergoes a dramatic transition when the debris cloud was prominent and enveloped most of the funnel cloud. The weak echo column (WEC) began to fill at lower levels as large amounts of debris were lofted into the circulation. The axis of minimum ρhv shifted to a radius just beyond the funnel cloud. A column of positive ZDR was collocated with the funnel surrounded by negative ZDR. The negative ZDR and low ρhv within the debris cloud were likely the result of some common debris alignment from wheat stems. The positive ZDR within the funnel signified the presence of a few hydrometeors.

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

“…Alternative explanations for the low r hv and high Z DR observations are presented in the following discussion. The relationship between debris size and/or concentration has been noted indirectly by several past studies in which increases in radar reflectivity and decreases in r hv coincide with the increased damage at the surface and/or higher wind speeds implying greater amounts of lofted debris (Bodine et al , 2014Van Den Broeke and Jauernic 2014;Wakimoto et al 2018). Ryzhkov et al (2005) noted that resonance scattering reduces r hv for larger scatterers compared to smaller scatterers.…”

“…Several pictures of the wall cloud associated with the Shawnee supercell were analyzed using photogrammetric techniques. Photogrammetry can be used to analyze photos quantitatively to determine angular measurements that can be converted into horizontal and vertical dimensions at the distance of a phenomenon of interest (e.g., Malkus 1952;Wakimoto and Martner 1992;Zehnder et al 2007). An example of a photogrammetric analysis for the current study will be presented in section 4a.…”

“…It is possible that the updraft may result in the accumulation of small debris at this height. Wakimoto et al (2015) documented the existence of a debris overhang that was produced by an updraft. The trend of the profiles above 2.5 km is reversed.…”

“…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.…”

“…The intense circulation associated with tornadoes results in strong centrifuging of hydrometeors and debris (e.g., Dowell et al 2005). This centrifuging can produce a positive bias in the tornado-relative radial velocities relative to the airspeed since Doppler radars are measuring the motion of the scatterers (e.g., Dowell et al 2005;Wakimoto et al 2012;Nolan 2013;Bodine et al 2014). The bias can lead to an anomalous divergent signature in Doppler velocities within the tornado at low levels where centrifuging is typically the most intense owing to a combination of larger debris particles and the strongest rotational velocities (e.g., Dowell et al 2005).…”