Tornado Intensity Research Articles

High-Temporal Resolution Observations of the 27 May 2015 Canadian, Texas, Tornado Using the Atmospheric Imaging Radar

Abstract On 27 May 2015, the Atmospheric Imaging Radar (AIR) collected high-temporal resolution radar observations of an EF-2 tornado near Canadian, Texas. The AIR is a mobile, X-band, imaging radar that uses digital beamforming to collect simultaneous RHI scans while steering mechanically in azimuth to obtain rapid-update weather data. During this deployment, 20°-by-80° (elevation × azimuth) sector volumes were collected every 5.5 s at ranges as close as 6 km. The AIR captured the late-mature and decaying stages of the tornado. Early in the deployment, the tornado had a radius of maximum winds (RMW) of 500 m and exhibited maximum Doppler velocities near 65 m s−1. This study documents the rapid changes associated with the dissipation stages of the tornado. A 10-s resolution time–height investigation of vortex tilt and differential velocity is presented and illustrates an instance of upward vortex intensification as well as downward tornado decay. Changes in tornado intensity over periods of less than 30 s coincided with rapid changes in tornado diameter. At least two small-scale vortices were observed being shed from the tornado during a brief weakening period. A persistent layer of vortex tilt was observed near the level of free convection, which separated two layers with contrasting modes of tornado decay. Finally, the vertical cross correlation of vortex intensity reveals that apart from the brief instances of upward vortex intensification and downward decay, tornado intensity was highly correlated throughout the observation period.

A Novel Model of Quasi-Stationary Vortices in the Earth’s Atmosphere

In the great variety of vortex motions in the atmosphere, concentrated vortices, attracting increased interest from the point of view of both fundamental research and practice, clearly stick out. A sufficiently precise definition of the concentrated vortex can be given for the case of an ideal fluid—it is an area localized in the space, surrounded by a potential flow and having a nonzero vorticity. Such vortices can be combined into a class of small-scale concentrated vortices including dust devils (DDs), waterspouts, fire vortices, and larger scale and more intense tornadoes. Unlike planetary-scale vortices (cyclones and anticyclones), DDs and tornadoes are small-scale vortices. DDs and tornadoes are generated in different environments (tornadoes occur in strong storm clouds), but they have much in common in regards to their structure. The speed of rotation in such vortices reaches the maximum value at a characteristic radius and tends to zero when approaching the center. The rotation speed in them has much in common with the rotation speed in stationary Rankine or Burgers vortices. This work is devoted to the study of a novel low-parameter model of stationary vortices. The model is most suitable for describing concentrated vortices in the Earth’s atmosphere. Within the framework of ideal hydrodynamics, a new model of thin vortex filaments is constructed at heights that are small when compared to the vertical scale of the Earth’s atmosphere. Unlike Rankine and Burgers vortices, it allows one to describe the structure limited in the radial direction. Quasi-stationary vortices in such a model arise as a result of the balance of two effects: the concentration of vertical vorticity to the center and the advection of the vortex motion in the vertical direction.

Comments on “The Regulation of Tornado Intensity by Updraft Width”

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Structural performance of multi-story mass-timber buildings under tornado-like wind field

Tall mass-timber buildings utilize engineered wood panels to form their main gravity and lateral load resisting systems, which makes them lighter and more flexible than buildings made from concrete, masonry or even steel.In general, drift sensitive components of tall mass-timber buildings could be susceptible to damages due to increased deflection when subjected to extreme wind storms like violent tornadoes. This paper assessed the structural performance of a multi-story mass-timber building, which was designed using the customary 1-in-50 years design wind speed of the 2010 National Building Code of Canada with a load factor of 1.4, under experimentally simulated tornado-like wind fields. In the study, wind loads were obtained from laboratory simulations of tornado-like wind field and atmospheric boundary layer flow at Western University, Canada. Tornadic wind loads from the laboratory tests were scaled to five Enhanced Fujita wind speeds, representing various levels of damage. Dynamic structural analyses were carried out in time-domain to include the possible amplification due to the dynamic component of the excitation and assess floor level inter-story drift and shear force demands for various parameters. The varied parameters were tornado intensity level, the orientation of the building (aerodynamic direction), and critical damping ratio. Based on the obtained results, the vulnerability of drift sensitive components of the study building under tornado-like wind field was estimated. It is shown that strong tornadoes may pose significant damage to drift sensitive non-structural components of multi-story mass-timber buildings. Finally, roadmaps to improve the design of mass-timber buildings in tornado-prone areas are forwarded.

Analysis of the 16 May 2015 Tipton, Oklahoma, EF-3 Tornado at High Spatiotemporal Resolution Using the Atmospheric Imaging Radar

Abstract In this study, data collected by the Atmospheric Imaging Radar (AIR) are analyzed in conjunction with WSR-88D data (KFDR) for a tornado near Tipton, Oklahoma, on 16 May 2015. The analysis presented herein utilizes PPIs from both radars, polarimetric data from KFDR, time–height plots from the AIR, and a ground-based velocity track display (GBVTD) analysis. This study is novel in that it uses high-resolution mobile radar data (update time of 6–7 s) in tandem with polarimetric data from KFDR in order to identify possible areas of debris, including a debris ring contained within the outer vortex circulation. Leveraging the high spatiotemporal resolution of the AIR with the polarimetric capability of KFDR leads to analysis of reflectivity distributions, debris lofting, kinematic changes, and oscillations in tornado intensity during a portion of the mature stage of the tornado, with a particular focus on the relationship between changes in the reflectivity field and dynamical changes around the tornado. Debris is lofted in a high-reflectivity concentric ring of increasing radius and height around the tornado over several minutes, within the outer weak-echo hole (WEH). Simultaneously, debris lofting and asymmetric reflectivity distribution around the WEH coincide with changes in vortex tilt on multiple occasions. In one instance, hydrometeor fallout appears to precede a possible descending reflectivity core. Using the GBVTD results, near-surface convergence intensifies at the same time and location as when the debris ring is lofted. Additionally, strengthening of the tornado via multiple modes of vertical evolution (i.e., bottom-up intensification over time vs simultaneous intensification throughout the lowest few hundred meters) is observed.

Recent northeast Italian tornado events: lesson learned for improving structures

Increasing intensity and frequency of tornadoes have been reported in Europe in the last decades, and in Italy, in particular in the northeast area, including Veneto, Friuli Venezia Giulia and Trentino Alto Adige. The public consciousness and the meteorological control of this risk are sufficiently established in the USA. The European continent and the northeast of Italy do not exhibit a similar state, although the tornado damages induced are increasing and becoming of economic relevance. Studies and research are diffused and have reached a detailed level, being able to correlate tornado intensity to a detailed damage state for a wide amount of building classes. But, codes and standard, both in USA and in the whole European continent, have not been developed for tornado loadings. For this reason, to fill the gap between studies, research and observational data, in this study Italian wind extreme events are presented and discussed first. In a second part, the damage assessment results of the most extreme events recorded in the northeast of Italy (from F3 to F5, Fujita scale) from 1905 to 2017 are presented. Codes and standard showing the lack of design and verification procedure are presented in the third part. Finally, a tornado-resistant building classification is presented to enforce the consciousness that new codes and standard could protect people from extreme events, decreasing dramatically the devastation of not so rare phenomena also for Italy.

Spatial and temporal analysis of the 27 April 2011 tornado outbreak in Central Alabama

This study investigates the spatial and temporal patterns of the 27 April 2011 tornado outbreak in Central Alabama. Disasters, and vulnerabilities to such events, vary across space and time. The 2011 Super Outbreak was the largest, most costly, and one of the most deadly tornado outbreaks ever recorded in U.S. history. In this study, the results of 29 documented tornado tracks (889 data points total) in Central Alabama reveal findings related to complex topography and its effects on tornado intensity and damage. The temporal patterns of this particular outbreak are consistent with other studies’ evidence that suggests a small peak in nocturnal tornado activity in the southeast U.S. These are a few of the many factors that contribute to tornado vulnerability in the Deep South.

What is the Worst That Could Happen? Reexamining the 24–25 June 1967 Tornado Outbreak over Western Europe

Abstract On 24–25 June 1967 one of the most intense European tornado outbreaks produced extensive damage (approximately 960 houses damaged or destroyed) and resulted in 232 injuries and 15 fatalities in France, Belgium, and the Netherlands. The 24–25 June 1967 tornado outbreak shows that Europe is highly vulnerable to tornadoes. To better understand the impact of European tornadoes and how this impact changed over time, the question is raised, “What would happen if an outbreak similar to the 1967 one occurred 50 years later in 2017 over France, Belgium, and the Netherlands?” Transposing the seven tornado tracks from the June 1967 outbreak over the modern landscape would potentially result in 24 990 buildings being impacted, 255–2580 injuries, and 17–172 fatalities. To determine possible worst-case scenarios, the tornado tracks are moved in a systematic way around their observed positions and positioned over modern maps of buildings and population. The worst-case scenario estimates are 146 222 buildings impacted, 2550–25 440 injuries, and 170–1696 fatalities. These results indicate that the current disaster management policies and mitigation strategies for Europe need to include tornadoes, especially because exposure and tornado risk is anticipated to increase in the near future.

1984 Ivanovo tornado outbreak: Determination of actual tornado tracks with satellite data

The 1984 Ivanovo tornado outbreak is one of the most fatal tornado events in Europe with previously unspecified tornado track characteristics. In this paper, we used Landsat images to discover tornado-induced forest disturbances and restore actual characteristics of tornadoes during the outbreak. We defined boundaries of tornado-induced windthrows by visual comparison of satellite images and specified them with Normalized Difference Infrared Index. We confirmed the occurrence of eight tornadoes during the outbreak and determined their location, path width and length. Other tornadoes occurrence during the outbreak was discussed. Fujita-scale intensity of confirmed tornadoes was estimated based on the related literature corpus including previously omitted sources. In addition, information on tornado path lengths and widths was used to estimate minimal tornado intensity for those tornadoes that passed no settlements. In total, the Ivanovo outbreak includes 8–13 tornadoes with F-scale rating mean ranges from 1.8–2.5 and has adjusted Fujita length around 540 km, which makes the outbreak one the strongest in Europe and places it within the upper quartile of U.S. outbreaks. Characteristics of certain tornadoes within the Ivanovo outbreak are exceptional for Russia. The widest tornado path during the Ivanovo outbreak is 1740 m; the longest is from 81.5–85.9 km. With the example of the Ivanovo outbreak, we showed that existing databases on historical Russian tornadoes tend to overestimate tornado path length (for very long tornadoes) and underestimate maximum tornado path width.

An empirical assessment of impact based tornado warnings on shelter in place decisions

In the spring of 2012, the United States’ National Weather Service implemented new impact based tornado warnings (IBWs) that include information about predicted storm impacts to improve the likelihood of one taking protective action. In addition to including more extreme language, IBWs for especially intense tornadoes include threat tags labeling the impact as “considerable” or “catastrophic.” Research by the author Casteel (2016) [3] showed that, when compared to non-IBWs, IBWs for low intensity tornadoes produced higher intentions of sheltering in place. The research reported here builds upon that earlier work. In four experiments, IBWs for stronger tornadoes are compared to those for weaker tornadoes, to assess whether the severe language used in the higher impact IBWs motivates higher sheltering intentions. Participants adopted the role of a plant manager tasked with keeping employees safe and read IBWs containing differing impact and severity language. At three decision points, the participants stated their likelihood of having employees shelter in place. In three of four experiments, the results show that any warning containing impact language stronger than a low intensity IBW, regardless of the presence of threat tags or extreme language, produced higher sheltering intentions. Additionally, sheltering decisions to “considerable” or “catastrophic” warnings did not differ in two experiments involving adult samples. These results suggest that the heightened risk transmitted by the stronger impact statements does communicate increased risk and that extreme language is not necessary to craft an effective tornado warning.

The Regulation of Tornado Intensity by Updraft Width

Abstract Strong to violent tornadoes cause a disproportionate amount of damage, in part because the width and length of a tornado damage track are correlated to tornado intensity (as now estimated through enhanced Fujita scale ratings). The tendency expressed in the observational record is that the most intense tornadoes are often the widest. Herein the authors explore the simple hypothesis that wide intense tornadoes should form more readily out of wide rotating updrafts. This hypothesis is based on an application of Kelvin’s circulation theorem, which is used to argue that the large circulation associated with a wide intense tornado is more plausibly associated with a wide mesocyclone. Because a mesocyclone is, strictly speaking, a rotating updraft, the mesocyclone width should increase with increasing updraft width. A simple mathematical model that is quantified using observations of mesocyclones supports this hypothesis, as do idealized numerical simulations of supercellular thunderstorms.

An Integrated Damage, Visual, and Radar Analysis of the 2015 Foshan, Guangdong, EF3 Tornado in China Produced by the Landfalling Typhoon Mujigae (2015)

Abstract This work presents an integrated damage, visual, and radar analysis of a tropical cyclone (TC) tornado that has not been documented as detailed as midlatitude tornadoes. On 4 October 2015, an enhanced Fujita 3 (EF3) tornado spawned into Typhoon Mujigae and hit Foshan, Guangdong Province, China. This tornado was generated in a minisupercell ∼350 km northeast of the TC center and lasted about 32 minutes, leaving a southeast-to-northwest damage swath 30.85 km long and 20–570 m wide. Near-surface wind patterns and the size of the tornado, juxtaposition of the condensation funnel with the damage swath and radar signatures, and consistency between near-surface wind speed estimated from visual observations and that estimated using EF scale were revealed based on ground and aerial surveys, radar and surface observations, photographs, and tornado videos. Tornado videos showed two occurrences of vertical subvortices followed by the formation of a horizontal vortex. Some features of the tornado, the parent supercell and mesocyclone, and the convective environment were compared to their U.S. counterparts. This work provides a case review of a tornado with the most comprehensive information ever in China. Damage indicators used to estimate the tornado intensity in this Chinese case were compared with those in the United States, demonstrating the potential applicability of the EF scale in tornado damage surveys outside the United States.

Sounding‐derived parameters associated with tornadic storms in Catalonia

ABSTRACTCatalonia, a southern Europe coastal region in the western Mediterranean basin, is regularly affected by severe local storms which every year produce an average of 5 tornadoes and 12 waterspouts, based on data recorded from 2000 to 2016. Despite these tornadoes mostly being weak – not exceeding EF1 on the enhanced Fujita (EF) damage intensity scale – they occasionally reach stronger intensities, posing an evident threat to population and socio‐economic activity, particularly in densely populated coastal conurbations such as Tarragona or Barcelona. This study provides analysis of upper air conditions that favour the formation of tornadic storms in the region, considering five different stations in Spain and France to build a database of 333 soundings which included 49 tornadic soundings, 104 waterspout soundings (WAT) as well as non‐tornadic thunderstorms and dry period soundings. For each one, 12 different parameters were calculated and analysed to test their potential capacity to discriminate non‐tornadic from tornadic environments and also to assess the feasibility of stratifying tornado intensity (EF0, and EF1 or stronger, on the EF scale). The results indicate that storm‐relative helicity for the layer 0–3 km, with a threshold value of 150 m2 s−2, wind shear for the same layer, with a threshold of 15 m s−1, and composite parameters such as the supercell composite parameter with a threshold of 1.2 and universal tornadic index with a threshold of 0.3 are all useful to distinguish between non‐tornadic thunderstorms and EF1 or stronger tornadic events. These results contribute to a better description of the climatology of upper air conditions that favour tornadic storms in the region and can also help operational weather forecasting and surveillance tasks, thus increasing situational awareness in severe convective weather events.

Volatility of Tornadogenesis: An Ensemble of Simulated Nontornadic and Tornadic Supercells in VORTEX2 Environments

Despite an increased understanding of the environments that favor tornado formation, a high false-alarm rate for tornado warnings still exists, suggesting that tornado formation could be a volatile process that is largely internal to each storm. To assess this, an ensemble of 30 supercell simulations was constructed based on small variations to the nontornadic and tornadic environmental profiles composited from the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2). All simulations produce distinct supercells despite occurring in similar environments. Both the tornadic and nontornadic ensemble members possess ample subtornadic surface vertical vorticity; the determinative factor is whether this vorticity can be converged and stretched by the low-level updraft. Each of the 15 members in the tornadic VORTEX2 ensemble produces a long-track, intense tornado. Although there are notable differences in the precipitation and near-surface buoyancy fields, each storm features strong dynamic lifting of surface air with vertical vorticity. This lifting is due to a steady low-level mesocyclone, which is linked to the ingestion of predominately streamwise environmental vorticity. In contrast, each nontornadic VORTEX2 simulation features a supercell with a disorganized low-level mesocyclone, due to crosswise vorticity in the lowest few hundred meters in the nontornadic environment. This generally leads to insufficient dynamic lifting and stretching to accomplish tornadogenesis. Even so, 40% of the nontornadic VORTEX2 ensemble members become weakly tornadic. This implies that chaotic within-storm details can still play a role and, occasionally, lead to marginally tornadic vortices in suboptimal storms.

Modeling the Excitation of Seismic Waves by the Joplin Tornado

AbstractTornadoes generate seismic signals when they contact the ground. Here we examine the signals excited by the Joplin tornado, which passed within 2 km of a station in the Earthscope Transportable Array. We model the tornado‐generated vertical seismic signal at low frequencies (0.01–0.03 Hz) and solve for the strength of the seismic source. The resulting source amplitude is largest when the tornado was reported to be strongest (EF 4–5), and the amplitude is smallest when the tornado was weak (EF 0–2). A further understanding of the relationship between source amplitude and tornado intensity could open up new ways to study tornadoes from the ground.

A satellite-derived climatology of unreported tornadoes in forested regions of northeast Europe

This study presents a novel method of tornado track identification in forested regions in Europe based on remote sensing data. The method enables an objective estimate (i.e. independent of population density and observational networks) of tornado climatology in forested regions. The method is based on the identification of narrow and elongated areas as forest disturbances obtained using Landsat satellite images and Landsat-based Global Forest Change (GFC) data. These areas were subsequently verified with high-resolution satellite images for verification of a tornadic cause of forest damage. Landsat and MODIS satellite images, weather station observations and reanalysis data were additionally involved in order to determine tornado dates. A minimum F-scale tornado intensity was estimated by a Weibull distribution model using information on tornado path lengths and widths. The method is applied to the forested regions of northeast Europe, where 110 tornado tracks were identified between the 2000 and 2014years, 105 of which were previously unreported and discovered for the first time. For some regions, tornado density estimates using the new method is 2–3 times higher than other previously published estimates. The largest number of tornadoes occurred in 2009, and June is the most favourable month for tornado formation (including strong tornadoes and tornado outbreaks). Most identified tornadoes have path length <10km with maximum and mean widths of approximately 200–300m and 100–200m, respectively. A few tornadoes with long and wide paths were found; four of them likely had F3 minimal intensity.

Tornado Hazard Assessment for a Nuclear Power Plant in China

Tornado is one of the most hazardous external natural events which should be taken into account in the siting, design and safety evaluation of nuclear power plants. The tornado hazard has been assessed for a nuclear power plant located in the Southeast China in this paper. Using the original Fujita scale and grading by a number of experts, intensities of the tornado segments have been determined. The design-basis tornado wind speed, parameters and missiles generated have been evaluated following the methodology listed in the hChinese Nuclear Safety Guide HAD101/10. The results show that the overall cumulative frequency and intensity of tornadoes in the site area is not in a logarithm-linear relationship. The expected annual tornado occurrence frequencies of various F scales have been estimated by fitting higher intensity samples. The resulting wind speed corresponding to an exceedance frequency of 10-7 per year seems to be sensitive to the fitting samples. Considering the uncertainties, the intensity and frequency of tornadoes in the survey area, the ultimate design-basis tornado wind speed is taken to be 70.4 m/s, which is the lower limit wind speed of F3 scale. Moreover current problems in tornado hazard assessment in China are discussed.

Polarimetric Radar Metrics Related to Tornado Life Cycles and Intensity in Supercell Storms

AbstractPolarimetric radar signatures have been related to the typical evolution of supercell storms, including through tornado life cycles. Now that polarimetric radar observations are available for a large sample of supercell storms, time series of new radar metrics can be derived. These metrics can be compared with phases of known tornado life cycles in an effort to develop new methods of anticipating tornadoes and to increase understanding of storm-scale structural and microphysical changes through supercell and tornado life cycles. In this paper, radar metrics including measures of differential reflectivity ZDR columns, ZDR arcs, polarimetrically inferred hailfall regions, and mean value of copolar correlation coefficient ρhv in the echo appendage are compared to the tornado life cycle and to storm-maximum tornado intensity in a sample of 35 tornadic supercells. It is shown that these radar metrics may change repeatedly and thus can be used to distinguish tornadic and nontornadic periods in single supercell storms, tornadogenesis from tornado demise times, and modes of storm evolution relative to tornadoes (e.g., if a storm produces one tornado or several). The polarimetric radar metrics are nearly as predictive of tornado intensity as commonly used measures of environmental variability for this sample.

The Impact of El Niño–Southern Oscillation (ENSO) on Winter and Early Spring U.S. Tornado Outbreaks

AbstractIn recent years, the potential of seasonal outlooks for tornadoes has attracted the attention of researchers. Previous studies on this topic have focused mainly on the influence of global circulation patterns [e.g., El Niño–Southern Oscillation (ENSO), North Atlantic Oscillation, or Pacific decadal oscillation] on spring tornadoes. However, these studies have yielded conflicting results of the roles of these climate drivers on tornado intensity and frequency. The present study seeks to establish linkages between ENSO and tornado outbreaks over the United States during winter and early spring. These linkages are established in two ways: 1) statistically, by relating raw counts of tornadoes in outbreaks (defined as six or more tornadoes in a 24-h period in the United States east of the Rocky Mountains), and their destructive potential, to sea surface temperature anomalies observed in the Niño-3.4 region, and 2) qualitatively, by relating ENSO to shifts in synoptic-scale atmospheric phenomena that contribute to tornado outbreaks. The latter approach is critical for interpreting the statistical relationships, thereby avoiding the deficiencies in a few of the previous studies that did not provide physical explanations relating ENSO to shifts in tornado activity. The results suggest that shifts in tornado occurrence are clearly related to ENSO. In particular, La Niña conditions consistently foster more frequent and intense tornado activity in comparison with El Niño, particularly at higher latitudes. Furthermore, it is found that tornado activity changes are tied not only to the location and intensity of the subtropical jet during individual outbreaks but also to the positions of surface cyclones, low-level jet streams, and instability axes.