Tornado Debris Research Articles

Polarimetric radar observations of the Jersey tornadic supercell on 1–2 November 2023

AbstractA large tornado and severe hailstorm struck Jersey, Channel Islands, just before midnight on 1–2 November 2023. Radar data are analysed to explore the morphology of the parent supercell thunderstorm. A tornado debris cloud was evident in polarimetric fields, collocated with a reflectivity ‘debris ball’. The debris cloud comprised a small region of exceptionally low correlation coefficient (<0.8) collocated with differential reflectivity ≤0dB. In vertical section, the debris signature comprised a column of low correlation coefficient and high reflectivity that tilted north‐northeast with height and extended to at least 2km above ground level.

Improving Estimation of Specific Differential Phase and Assessing Differential Backscattering Phase

Abstract Polarimetric variables such as differential phase ΦDP and its range derivative, specific differential phase KDP, contain useful information for improving quantitative precipitation estimation (QPE) and microphysics retrieval. However, the usefulness of the current operationally utilized estimation method of KDP is limited by measurement error and artifacts resulting from the differential backscattering phase δ. The contribution of δ can significantly influence the ΦDP measurements and therefore negatively affect the KDP estimates. Neglecting the presence of δ within non-Rayleigh scattering regimes has also led to the adoption of incorrect terminology regarding signatures seen within current operational KDP estimates implying associated regions of unrealistic liquid water content. A new processing method is proposed and developed to estimate both KDP and δ using classification and linear programming (LP) to reduce bias in KDP estimates caused by the δ component. It is shown that by applying the LP technique specifically to the rain regions of Rayleigh scattering along a radial profile, accurate estimates of differential propagation phase, specific differential phase, and differential backscattering phase can be retrieved within regions of both Rayleigh and non-Rayleigh scattering. This new estimation method is applied to cases of reported hail and tornado debris, and the LP results are compared to the operationally utilized least squares fit (LSF) estimates. The results show the potential use of the differential backscattering phase signature in the detection of hail and tornado debris.

Radar Characteristics and Causal Analysis of Two Consecutive Tornado Events Associated with Heavy Precipitation during the Mei-Yu Season

This paper comprehensively analyzed two consecutive tornado events associated with heavy precipitation during the Mei-yu season (a period of continuous rainy weather that occurs in the middle and lower reaches of the Yangtze River in China from mid-June to mid-July each year) and detailed the formation and development process of the tornadoes using Doppler weather radar, wind profiler radar, ERA5 reanalysis data, ground automatic station data and other multi-source data. The results showed that: (1) Small-scale vortices were triggered and developed during the eastward movement of the low vortex, forming two tornadoes successively on the eastern section of the Mei-yu front. (2) The presence of a gap on the front side of the reflectivity factor profile indicated that strong incoming airflow entered the updraft. Mesocyclones were detected with decreasing heights and increasing shear strengths. The bottom height of the tornado vortex signature (TVS) dropped to 0.7 km, and the shear value increased to 55.4 × 10−3 s−1. Tornado debris signatures (TDSs) could be seen with a low cross-correlation coefficient (CC) value area of 0.85–0.9 in the mesocyclone. The difference between the lowest-level difference velocity (LLDV) and the maximum difference velocity (MXDV) reached the largest value when a tornado occurred. (3) The continuously enhanced low-level jet propagated downward to form a super-low-level jet, and the strong wind direction and wind speed convergence in the boundary layer created a warm, moist and unstable atmosphere in Suzhou. With the entrainment of dry air, the northwest dry jet and the southeast moist jet stimulated the formation of a miniature supercell. (4) The low-level vertical wind shear of 0–1 km increased significantly upon tornado occurrence, which was more conducive to the formation and intensification of horizontal vorticity tubes. Encountering updrafts and downdrafts, the vorticity tubes might have been stretched and intensified. The first lightning jumps appeared 15 min and 66 min earlier than the Kunshan Bacheng tornado and the Taicang Liuhe tornado. The Liuhe tornado occurred during the stage when the lightning frequency reached its peak and then fell back.

Dual-Polarization Radar Observations of the Evolution of a Supercell Tornado and Analysis of the Echo Mechanisms

To gain a deeper understanding of the structural and evolutionary characteristics of supercell tornadoes that occurred in eastern China on 14 May 2021, observations from the S-band dual-polarization radars, soundings and other instruments are used to investigate the evolutionary process of the tornado formation by the mergering and strengthening of supercell storms. The results are described as follows. The updraft by upper divergence and vertical thermal instability induced by the cold source at the tropopause provided the environmental conditions suitable for tornado formation. The tornado event involved three storm merger processes, each of which was associated with an increase in the echo intensity, vertical rising speed, and vertical vorticity of the supercell. Furthermore, during the last merger, the merging of the two vortices resulted in the reduction of the rotation radius of the new vortex, which also provided a favorable condition for tornadogenesis. A schematic was proposed to describe storm mergers. The characteristics of the velocity spectrum width were indicative of the occurrence and evolution of the tornado in this case. During the tornado stage, distinct polarimetric variable signatures (e.g., a tornado debris signature and a differential reflectivity arc) and radial velocity signatures (i.e., a tornadic vortex signature) were observed.

Tornadoes in Hurricane Harvey

AbstractTropical cyclone tornadoes pose a unique challenge to warning forecasters given their often marginal environments and radar attributes. In late August 2017 Hurricane Harvey made landfall on the Texas coast and produced 52 tornadoes over a record-breaking seven consecutive days. To improve warning efforts, this case study of Harvey’s tornadoes includes an event overview as well as a comparison of near-cell environments and radar attributes between tornadic and nontornadic warned cells. Our results suggest that significant differences existed in both the near-cell environments and radar attributes, particularly rotational velocity, between tornadic cells and false alarms. For many environmental variables and radar attributes, differences were enhanced when only tornadoes associated with a tornado debris signature were considered. Our results highlight the potential of improving warning skill further and reducing false alarms by increasing rotational velocity warning thresholds, refining the use of near-storm environment information, and focusing warning efforts on cells likely to produce the most impactful tornadoes.

Analysis of Debris Signature Characteristics and Evolution in the 24 May 2016 Dodge City, Kansas, Tornadoes

AbstractOn 24 May 2016, a supercell that produced 13 tornadoes near Dodge City, Kansas, was documented by a rapid-scanning, X-band, polarimetric, Doppler radar (RaXPol). The anomalous nature of this storm, particularly the significant deviations in storm motion from the mean flow and number of tornadoes produced, is examined and discussed. RaXPol observed nine tornadoes with peak radar-derived intensities (ΔVmax) and durations ranging from weak (~60 m s−1) and short lived (<30 s) to intense (>150 m s−1) and long lived (>25 min). This case builds on previous studies of tornado debris signature (TDS) evolution with continuous near-surface sampling of multiple strong tornadoes. The TDS sizes increased as the tornadoes intensified but lacked direct correspondence to tornado intensity otherwise. The most significant growth of the TDS in both cases was linked to two substantial rear-flank-downdraft surges and subsequent debris ejections, resulting in growth of the TDSs to more than 3 times their original sizes. The TDS was also observed to continue its growth as the tornadoes decayed and lofted debris fell back to the surface. The TDS size and polarimetric composition were also found to correspond closely to the underlying surface cover, which resulted in reductions in ZDR in wheat fields and growth of the TDS in terraced dirt fields as a result of ground scouring. TDS growth with respect to tornado vortex tilt is also discussed.

Tornado Debris from the 23 May 2017 “Tybee Tornado”

AbstractWe examine the trajectories of four historical markers displaced during an enhanced Fujita scale 2 (EF2) tornado at the Fort Pulaski National Monument located on Cockspur Island, east of Savannah in southeast Georgia. The careful work of National Park Service employees in cataloguing the origin and landing points of the debris allows for an unusually accurate analysis of tornado debris trajectories for heavy objects. These markers, weighing around 68 kg (150 lb) each, traveled intact for distances of up to 220 m (750 ft). One of the historical markers was fractured into at least three pieces, the larger of which traveled 300 m (1,000 ft). Understanding the travel for these relatively heavy items is important, as they are similar in weight to household appliances that could commonly be part of a tornado debris field.

A Multiscale Overview of the El Reno, Oklahoma, Tornadic Supercell of 31 May 2013

Abstract On 31 May 2013 a broad, intense, cyclonic tornado and a narrower, weaker companion anticyclonic tornado formed in a supercell in central Oklahoma. This paper discusses the synoptic- and mesoscale environment in which the parent storm formed, based on data from the operational network of surface stations, rawinsondes, and WSR-88D radars, and from the Oklahoma Mesonet, a Doppler radar wind profiler, Rapid Refresh (RAP) analyses, and photographs. It also documents the overall behavior of the tornadoes and their relationships to features in their parent supercell based on data from a nearby, rapid-scan, polarimetric, mobile Doppler radar. The supercell formed near the intersection of a cold front and a dryline in an environment of moderately strong vertical shear and high CAPE, at the southern end of a line of multicell convective storms. The tornado damage path was as wide as 4.2 km according to the NWS damage assessment and ground-relative Doppler velocities of at least 135 m s−1 were found at the theoretical beam height of <20 m AGL. The tornado debris signature in the copolar cross-correlation coefficient ρhv was as wide as ~4–5 km. After the strong tornado formed, at least one additional cyclonic tornado formed and rotated cyclonically around the main tornado; it was then absorbed by it and the main tornado broadened. Smaller subvortices, which rotated cyclonically around a common axis of rotation, were subsequently observed. The tornado then weakened but remained broad, while the anticyclonic tornado formed to the southeast along the rear-flank gust front.

An Integrated Damage, Visual, and Radar Analysis of the 2013 Moore, Oklahoma, EF5 Tornado

An integrated damage, visual, and radar analysis of the EF5 Moore, Oklahoma, tornado that occurred on 20 May 2013 is presented. Characteristics of the damage path are discussed based on detailed ground and aerial surveys. Tree fall reveals highly convergent surface flow over the majority of the damage path. At times, the convergent flow is observed at radii less than that of the condensation funnel. A photogrammetric analysis of still photos and video shows that the damaging winds extend well beyond the condensation funnel location. The condensation funnel often coincides with the EF1, EF2, and EF3 isopleths. Observations of the tornado debris signature (TDS) by the Twin Lakes (KTLX)–Weather Surveillance Radar-1988 Doppler (WSR-88D) are presented. The TDS is not a good indicator of tornado intensity just after tornadogenesis. The spatial relationship between the TDS, condensation funnel, and damage path is highlighted. An analysis of the area encompassed by the respective EF-scale isopleths is presented t...

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 damage-based 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−1 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.

Dual-Wavelength Polarimetric Radar Analyses of Tornadic Debris Signatures

AbstractStatistical properties of tornado debris signatures (TDSs) are investigated using S- and C-band polarimetric radar data with comparisons to damage surveys and satellite imagery. Close proximity of the radars to the 10 May 2010 Moore–Oklahoma City, Oklahoma, tornado that was rated as a 4 on the enhanced Fujita scale (EF4) provides a large number of resolution volumes, and good temporal and spatial matching for dual-wavelength comparisons. These comparisons reveal that S-band TDSs exhibit a higher radar reflectivity factor (ZHH) and copolar cross-correlation coefficient (ρhv) than do C-band TDSs. Higher S-bandρhvmay result from a smaller ratio of non-Rayleigh scatterers to total scatterers due to the smaller electrical sizes of debris and, consequently, reduced resonance effects. A negativeZDRsignature is observed at 350 m AGL at both the S and C bands as the tornado passes over a vegetated area near a large body of water. Another interesting signature is a positive (negative) shift in propagation differential phase (ΦDP) at S band (C band), which could result from increased phase folding at C band. With increasing height above 350 m AGL, the S- and C-bandZHHdecreases andρhvincreases, indicating a decrease in debris size. To investigate relationships between polarimetric variables and tornado wind fields, range profiles of radial and tangential wind speeds are obtained using two radars. Velocity profiles reveal radial divergence within vortex core flow through 700 m AGL collocated with the TDS. Formation of a weak-echo hole and higherρhvin the vortex center aloft suggests debris centrifuging, outward motion of scatterers due to radial divergence (i.e., two-cell vortex flow), or both.

Safe Room Wall Design for Tornado Survival

Safe room is a reinforced structure specially designed to meet the Federal  Emergency Management Agency (FEMA) criteria and provide protection in extreme weather events, including tornadoes and hurricanes. The materials used for safe room walls are expected to resist loads imposed and tornado debris impact. Tornadoes rated as high as EF-5 can create maximum wind speeds of more than 300 mph, which is enough to demolish any structures in their path. These maximum wind speeds produce forces that are about twice as large as those produced by the strongest hurricanes. One of the common safe room wall designs is made of plywood/steel-plate composite. The main objective of this paper is to use a finite element simulation code, LS-DYNA, to predict the dynamic response of plywood when impacted by tornado missiles such as 2 x 4 wood timbers.

Tornado Debris Characteristics And Trajectories During The 27 April 2011 Super Outbreak As Determined Using Social Media Data

Using publicly available information gleaned from over 1700 found-and-returned objects on the “Pictures and Documents found after the 27 April 2011 Tornadoes” Facebook page, the authors have created a database of 934 objects lofted by at least 15 different tornadoes during the 27 April 2011 Super Outbreak in the southeast United States. Analysis of the takeoff and landing points of these objects using GIS and high-resolution numerical trajectory modeling techniques extends previous work on this subject that used less specific information for much smaller sets of tracked tornado debris. It was found that objects traveled as far as 353 km, exceeding the previous record for the longest documented tornado debris trajectory. While the majority of debris trajectories were 10° to the left of the average tornado track vector, the longest trajectories exhibited a previously undocumented tendency toward the right of the average tornado track vector. Based on results from a high-resolution trajectory model, a relati...

An Analysis of Vortices Embedded within a Quasi-Linear Convective System Using X-Band Polarimetric Radar

Abstract On 2 April 2010, a developing quasi-linear convective system (QLCS) moved rapidly northeastward through central Oklahoma spawning at least three intense, mesoscale vortices. At least two of these vortices caused damage rated as category 0 to 1 on the enhanced Fujita scale (EF0–EF1) in and near the town of Rush Springs. Two radar networks—the National Weather Service Weather Surveillance Radar-1988 Doppler network (WSR-88D) and the Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) radar network—collected high spatial and temporal resolution data of the event. This study is an in-depth polarimetric analysis of mesovortices within a QLCS. In this case study, the storm development and evolution of the QLCS mesovortices are examined. Significant findings include the following: 1) The damage in Rush Springs was caused by a combination of the fast translation speed and the embedded circulations associated with QLCS vortices. The vortices’ relative winds nearly negated the storm motion to the left of the vortex, but doubled the ground-relative wind to the right of the vortex. 2) A significant differential reflectivity (ZDR) arc developed along the forward flank of the first vortex. The ZDR arc propagated northeastward along the QLCS with the development of each new vortex. 3) A minimum in the copolar correlation coefficient (ρhv) in the center of the strongest vortex was observed, indicating the likely existence of a polarimetric tornado debris signature (TDS). A secondary ρhv minimum also was found just to the right of the vortex center, possibly associated with lofted debris from straight-line winds.

Effects of Finescale Debris on Near-Surface Tornado Dynamics

Debris clouds provide an important visual signature of tornadoes and can potentially significantly affect the wind structure, damage potential, and Doppler radar measurements of tornado wind speeds. To study such issues, the dynamics of finescale debris have been added to an existing high-resolution large-eddy simulation model of tornado dynamics. A so-called “two-fluid” or “Eulerian–Eulerian” approach is employed, together with a surface layer model for lofting and depositing debris. In this paper the debris implementation is described, three critical dimensionless parameters governing tornado debris effects are identified, and sample results from a large set of simulations of tornadoes with idealized debris are presented. The results demonstrate that the accumulation of small-scale debris within the surface layer and corner flow can significantly alter the wind speeds and flow structure of the tornado vortex within a few hundred meters of the surface. They suggest that the total mass of the debris cloud can reach tens of thousands of tons. Near the surface, the debris mass loading can be well above 1, the peak mean velocities can be reduced by as much as half, and the total momentum (air plus debris) can either significantly increase or decrease. Local air and debris velocities can differ significantly and in a nontrivial fashion, thereby complicating the interpretation of Doppler radar measurements of tornado structure. Debris fluctuations, centrifuging, negative buoyancy, and angular momentum transport are all significant mechanisms for the debris effects. A negative physical feedback reduces the sensitivity of the results to changes in the parameterization of the surface debris fluxes. The realistic simulation of tornado debris clouds and surface damage tracks should prove useful in identifying the dynamics governing their observed counterparts.

Eumycotic mycetoma caused by Cladophialophora bantiana in a patient with systemic lupus erythematosus

We present the case of a 31-year-old patient who developed widespread mycetoma across her back and shoulders caused by Cladophialophora bantiana 16 years after injury to those sites from tornado debris. The patient also had a history of systemic lupus erythematosus treated with systemic steroids. Systemic antifungal treatment with fluconazole and itraconazole proved ineffective, and surgical debridement was required. Nine other culture-confirmed cases of cutaneous infection with this organism have been reported worldwide. This type of infection can occur in immunocompromised or immunocompetent patients, and may respond to systemic antifungals or surgery.

A History of Severe-Storm-Intercept Field Programs

Abstract Efforts to study severe convective storms and tornadoes by intercepting them either on the ground or on airborne platforms are highlighted. Airborne sorties into or near waterspouts in the Florida Keys with instruments were made in the late 1960s and the 1970s. The main goals of the first organized ground-based severe storm intercept field programs in the 1970s at the National Severe Storms Laboratory and at the University of Oklahoma were to verify severe weather signatures detected by a remote Doppler radar, to identify cloud features that could aid storm spotters, and to estimate wind speeds in tornadoes based on the photogrammetric analysis of tornado debris movies. Instruments were subsequently developed that could be carried along on intercept vehicles to measure in situ electric field change, thermodynamic variables, and wind, near the ground and aloft. Beginning in the late 1980s, portable and mobile Doppler radars were developed that could be used to make estimates of the maximum wind sp...

Long-Distance Debris Transport by Tornadic Thunderstorms.Part I: The 7 May 1995 Supercell Thunderstorm

Abstract On 7 May 1995, during VORTEX 95, the Tornado Debris Project at the University of Oklahoma collected debris transported up to 190 km (120 mi) in association with an isolated tornadic thunderstorm which moved over north Texas and southern/central Oklahoma. Analysis of WSR-88D radar reflectivity data along with eyewitness accounts suggest that plumes observable in the radar reflectivity field contained debris that were transported long distances by this storm. The three main clusters of debris can be explained by at least three different modes of deposition: rear-flank deposition, left-flank deposition, and forward-flank deposition. Trajectory estimates outside the storm based on terminal fall speeds of the collected debris suggest much of the debris did not travel as far as it would if it had left the storm at upper levels in a dry state. Direct and indirect precipitation effects are diagnosed as potential factors limiting the distance transported.