Thunderstorm Wind Research Articles

Diurnal and Seasonal Patterns of Convective Weather Hazards in Tennessee and Their Potential to Cause Harm (1996–2022)

Flash floods, tornadoes, and nontornadic thunderstorm winds occur across Tennessee throughout the year, some causing harm to residents of the state. This work used data from the National Centers for Environmental Information Storm Events Database (1996–2002) to assess the frequency of hazardous and harmful––those that resulted in one direct injury and/or fatality––events across the state and determine how their frequency varied seasonally and diurnally. Hazards were most common and most harmful in Middle Tennessee and densely populated counties. Chi-square tests identified differences in hazardous and harmful event occurrences between seasons and from day to night. These relationships were further described in a logistic regression model, which indicated that a tornado or nighttime event was significantly more likely to result in reported harm, and a nontornadic thunderstorm wind or summer event was less likely to result in such a report. There are likely some reporting biases that affect these results, for example the underreporting of overnight events that do not cause harm. Overall, these findings suggest that, in Tennessee, annual and diurnal patterns in the overall hazard climatology differ from the patterns of reportedly harmful events, and point to the danger of convective hazards occurring at night.

On a modified definition of a derecho. Part I: Construction of the definition and quantitative criteria for identifying future derechos over the contiguous U.S.

Abstract The definition of a derecho has been modified to require hurricane-force (33+ m s−1) gusts, a staple for destructive wind events in earlier derecho studies. The new proposed definition states that the derecho is a widespread severe windstorm characterized by a family of destructive downbursts containing hurricane-force gusts, and is associated with an extra-tropical, cold-pool-driven Mesoscale Convective System. Derecho identification is performed with the use of an algorithm, rendering this study among the first to identify derechos objectively. Through sensitivity tests and qualitative analyses, we propose that the term derecho be used for thunderstorm wind swaths that have path lengths of at least 400 km, with no more than 1-h or 200-km (temporal or spatial, respectively) gaps allowed between wind reports, with at least five reports of 33+ m s−1 wind gusts, separated by 80 km, required for derecho identification. To account for possible overestimation of wind speeds, at least three 33+ m s−1 thunderstorm wind gust reports, separated by 80 km, need to be measured.

The –WIND RISK project: nowcast and simulation of thunderstorm outflows

–WIND RISK is a research project dealing with measurement and modelling of wind fields within thunderstorm cumulonimbus clouds and outflows at the ground (i.e., downbursts and gust fronts). The general objective of the project is to advance the knowledge about the processes occurring inside thunderstorm clouds responsible for strong outflows, and the identification of the environmental (synoptic and meso-scale) conditions favourable to their development. The area under investigation is Northwestern Italy and the Ligurian Sea, which are among the most exposed regions to strong thunderstorms in Europe. Two measurement campaigns using Doppler weather radars and remote-sensing ground-based anemometry, and ad-hoc simulations using the WRF model are carried out to build a database of thunderstorm wind fields with special focus on downdraft and downburst characterization. All measurements and simulations are shared within the scientific community after the end of the project through datasets published on open access platforms.

Dynamic Response Analysis of Moving Trains Passing Through the Stationary Thunderstorm Downburst Wind

The safety of the high-speed train traveling through the stationary thunderstorm downburst wind was studied. First, a thunderstorm wind test device was used to simulate the stationary thunderstorm downburst wind. Based on the rigid model pressure measurement tests, the aerodynamic forces of the train traveling along different paths through the stationary thunderstorm downburst wind were measured. The influence of the radial distance of the crossing path on the aerodynamic force coefficients of the train was investigated. On this basis, an unsteady aerodynamic model of the high-speed train crossing through the stationary thunderstorm downburst wind was established, and dynamic response analysis was carried out using the SIMPACK multibody dynamics simulation software to explore further the safety of the high-speed train crossing through the stationary thunderstorm downburst wind. The research showed that the stationary thunderstorm downburst wind field has significant spatial variation characteristics compared with the atmospheric boundary layer wind field. When the train passes through the thunderstorm downburst wind, the radial wind speed and wind yaw angle experienced by the train constantly change, and the change curve shows a symmetrical distribution. The aerodynamic force of the train will undergo sudden loading and unloading processes, and the lateral force coefficient of the train on different paths shows a “pulse-type” variation. Moreover, the lateral force coefficient increases with the increase of wind yaw angle. Under the influence of the thunderstorm downburst wind, the variation trend of the aerodynamic force coefficients of the train is consistent with that under crosswind. However, there are significant differences in the numerical values. Therefore, it is impossible to simply use the formula for calculating the aerodynamic force coefficients of the train under crosswinds to predict the aerodynamic force coefficients of the train under the thunderstorm downburst wind. While passing through the thunderstorm downburst wind, the overturning coefficient index plays a decisive role in the safety of train operations. Train rollover is the main form of train safety accidents, while derailment accidents are not easy. The numerical results obtained in this study are significant for evaluating the operational safety while moving trains traversing the stationary thunderstorm downburst wind.

The influence of thunderstorm type on extreme near-surface wind speeds: Iowa case study

The derecho of August 10, 2020 that impacted Iowa and neighboring states is the costliest thunderstorm disaster in U.S. history. A derecho, which features prolonged and destructive winds, is a type of thunderstorm which has different near-surface wind generating mechanisms than typically assumed in wind engineering. The derecho event prompted two research questions with respect to wind engineering: (1) should derechos, and more broadly thunderstorm type, be considered separately? and (2) how unique is this particular derecho event?Wind speeds for design in the U.S. are currently estimated using an approach where probability distributions of all thunderstorm winds are analyzed through a mixed distribution. Using Automated Surface Observing System (ASOS) and radar data from the National Weather Service, thunderstorm events with ASOS wind speeds >58 mph (26 m/s) were classified by thunderstorm type: single-cell, multicellular, or supercell thunderstorms in Iowa. An extreme value analysis was done on each thunderstorm type. Multicellular thunderstorms, like the August 2020 derecho, dominate the extreme wind climatology in Iowa. Evaluating the uniqueness of the derecho event required a post-damage assessment. Analysis from failed and unfailed street signs and nearby anemometry was used to estimate peak wind speeds approaching 120 mph (50 m/s).

Atmospheric conditions conducive to thunderstorms with downbursts in Canada and a downburst precursor parameter

Thunderstorm winds are the costliest wind hazard in Canada, but they have not been well studied. This paper investigates atmospheric conditions prone to downbursts in Canada using a combination of reported downbursts from damage survey reports, ERA5 reanalysis data, lightning flash observations, radar imagery, and upper air measurements for the period of 2019–2023. We propose a novel Downburst Precursor Parameter (DPP) by integrating two low-correlated thermodynamic and kinematic parameters. DPP outperforms other existing instability indices in downburst diagnosis in Canada. Our spatial analysis reveals the absence of damaging downbursts west of the Rockies, while approximately half of all recorded damaging downbursts occurred in southeastern Canada. Squall lines and supercells are the most common types of downburst-generating storms in Canada. Furthermore, nearly two-thirds of storms are squall lines when a downburst is accompanied by lightning flashes, which occurred in ∼71% of all cases. The remaining ∼29% of downbursts without lightning are mostly dry downbursts, typically displaying a disorganized pattern of convective storms on a radar screen. The equivalent potential temperature difference between the surface and mid-level in the troposphere (∆θe) exceeds 13 K prior to 61% of damaging downbursts. This result indicates that ∆θe might be a useful downburst indicator in Canada despite lower values compared to many regions in the United States.

A Machine Learning Approach to Improve the Usability of Severe Thunderstorm Wind Reports

Abstract Many concerns are known to exist with thunderstorm wind reports in the National Center for Environmental Information Storm Events Database, including the overestimation of wind speed, changes in report frequency due to population density, and differences in reporting due to damage tracers. These concerns are especially pronounced with reports that are not associated with a wind speed measurement, but are estimated, which make up almost 90% of the database. We have used machine learning to predict the probability that a severe wind report was caused by severe intensity wind, or wind ≥ 50 kt (∼25 m s−1). A total of six machine learning models were trained on 11 years of measured thunderstorm wind reports, along with meteorological parameters, population density, and elevation. Objective skill metrics such as the area under the ROC curve (AUC), Brier score, and reliability curves suggest that the best performing model is the stacked generalized linear model, which has an AUC around 0.9 and a Brier score around 0.1. The outputs from these models have many potential uses such as forecast verification and quality control for implementation in forecast tools. Our tool was evaluated favorably at the Hazardous Weather Testbed Spring Forecasting Experiments in 2020, 2021, and 2022.

Experimental translating downbursts immersed in the atmospheric boundary layer

Thunderstorm winds are cold descending gravity currents whose impingement on the ground creates strong radial outflows with maximum wind speeds in the near-ground region. They represent one of the greatest hazards for natural and built environment as well as one of the deadliest phenomena all over the world. This study carries on the post-processing analyses of the downburst experimental campaign performed at the WindEEE Dome, at Western University in Canada, in the context of the ERC project THUNDERR. While a former study presented the interaction between downburst and atmospheric boundary layer (ABL) winds, here the focus is on the influence exerted by the thunderstorm cloud translation. This was experimentally replicated at large scale by means of impinging jet technique where the jet axis was inclined to a non-zero angle with respect to the vertical. Finally, the inclusion of background ABL wind allowed to reconstruct the complete three-dimensional and non-stationary nature of the phenomenon. The outflow radial symmetry is lost in case of inclined jet axis. This leads to an intensification of the front-wind side and weakening of the rear-wind side, where the entrainment of the counter-directed ABL wind, and consequent flow speed-up, are not as pronounced as in the vertical-axis case. The non-linearity of the complex interaction between downburst, ABL flow and cloud translation is proven and quantified. Vertical profiles of mean wind speed and turbulence intensity are discussed in relation to the mutual interaction among flow components.

Wind field and pressure characteristics on wind turbine surface under moving thunderstorms

Based on computational fluid dynamics and large-eddy simulation technologies, a numerical simulation method of a moving thunderstorm field is established by considering the impinging jet model. In addition, the influence of movement speed of the storm center and jet velocity changes on the characteristics of the wind field is presented. By drawing horizontal wind speed radial profile curves, the vertical profile curves of horizontal wind velocity, radial wind profile curves of vertical wind speed, and transient wind speed characteristics of a moving thunderstorm downburst are illustrated. The results demonstrate that the wind field of a moving thunderstorm exhibits clear asymmetric characteristics. As the height from the ground increases, the horizontal wind speed first increases and then decreases. The extreme value of the horizontal wind speed appears at the position of (0.01–0.03) Djet (where Djet is the jet spout diameter) near the ground, which is consistent with the characteristics of a static thunderstorm wind field. Simultaneously, the distribution characteristics of wind pressure on the surface of wind turbines under moving thunderstorms is further studied. By considering variations of the wind attack angle, jet velocity, and moving speed, the results of wind pressure on the tower and blades of the wind turbine are presented. The coupling of the moving speed and jet velocity has a significant influence on the wind field and pressure on the wind turbine surface.

Environmental Parameter Analysis during the Extreme Damaging Gale that Hit the East Coast of the Shandong Peninsula

In this study, sounding data were used to investigate the environmental parameters of the eastern Shandong coast. June was the month with the most extreme thunderstorm winds, according to the results. Several parameters, which can be referenced in daily forecasts and early warnings, are indicative of extreme thunderstorms and gales. Strong convective storms are often the cause of extreme gales. Usually, there must be moderate to strong vertical wind shear conditions. The wet layer does not need to be excessively thick, but there is a very distinct dry layer with strong entrainment potential in the middle layer.

Analyzing, modelling, and simulating nonstationary thunderstorm winds in two horizontal orthogonal directions at a point in space

Thunderstorm winds in the horizontal plane are time-varying, resulting in the time-varying alongwind direction and mean wind speed in the alongwind direction. The fluctuating winds in the alongwind and crosswind directions are time-varying as well. The characterization of the mean and fluctuating winds for their simulation in two horizontal orthogonal directions are incomplete or unavailable in the literature. In the present study, we analyze and model the thunderstorm winds with respect to their time- and directional-variation of the alongwind speed and direction, as well as the fluctuating wind components in the alongwind and crosswind directions. For the analysis, we use the continuous harmonic wavelet. We show that the power spectral density (PSD) functions of the fluctuating winds depend on the time-varying mean wind speed. Based on the time-frequency spectral analysis, we propose the PSD functions and lagged coherence functions for the fluctuating thunderstorm winds in the alongwind and crosswind directions. We also present new empirical models for the time-varying alongwind direction and mean wind speed in the alongwind direction. Finally, we suggest the steps to simulate the wind speed in the alongwind and crosswind directions with time-varying directions and provide numerical examples to illustrate the effectiveness of our proposed models.

Thunderstorm gust response factor: General tendencies and sensitivity analysis

This paper aims to provide a sensitivity analysis of the thunderstorm gust response factor. The study is based on the extension of the gust response factor technique to the assessment of the maximum dynamic response of structures to thunderstorm outflows, starting from an evolutionary spectral model of the thunderstorm wind speed. The thunderstorm evolutionary spectral model depends on the modulating function of the slowly-varying mean speed, which is a function of two parameters, i.e. the background mean wind speed and the duration of the intense phase of the outflow. Starting from 129 full-scale thunderstorm records, the parameters of three different analytical models of the modulating function are extracted and a statistical analysis is carried out defining their range of variation. The dependence of the gust response factor on the analytical expression of the modulating function is studied as well as its sensitivity to the parameters of the function. Results show that the dependence of the gust response factor on the analytical expression of the modulating function is negligible, while it is very sensitive to the variation of the background wind and duration of the intense phase, especially for flexible and lowly-damped systems.

Retrieval of Peak Thunderstorm Wind Velocities Using WSR-88D Weather Radars

Abstract The current study develops a variant of the VAD method to retrieve thunderstorm peak event velocities using low-elevation WSR-88D radar scans. The main challenge pertains to the localized nature of thunderstorm winds, which complicates single-Doppler retrievals as it dictates the use of a limited spatial scale. Since VAD methods assume constant velocity in the fitted section, it is important that retrieved sections do not contain background flow. Accordingly, the current study proposes an image processing method to partition scans into regions, representing events and the background flows, that can be retrieved independently. The study compares the retrieved peak velocities to retrievals using another VAD method. The proposed technique is found to estimate peak event velocities that are closer to measured ASOS readings, making it more suitable for historical analysis. The study also compares the results of retrievals from over 2600 thunderstorm events from 19 radar–ASOS station combinations that are less than 10 km away from the radar. Comparisons of probability distributions of peak event velocities for ASOS readings and radar retrievals showed good agreement for stations within 4 km from the radar while more distant stations had a higher bias toward retrieved velocities compared to ASOS velocities. The mean absolute error for velocity magnitude increases with height ranging between 1.5 and 4.5 m s−1. A proposed correction based on the exponential trend of mean errors was shown to improve the probability distribution comparisons, especially for higher velocity magnitudes.

Variation Characteristics of the Wind Field in a Typical Thunderstorm Event in Beijing

The understanding of wind field characteristics during thunderstorms is key to structural design for resistance to thunderstorms. In this paper, the directional thunderstorm wind model is adopted to analyze the characteristics of vertical variations of the wind field in a typical thunderstorm event in the Beijing urban area, based on the measured data. First, the longitudinal and lateral fluctuating wind speed components were decoupled and the change of direction was obtained. Then, variation of the wind speed, wind direction, turbulence intensity, turbulence integral length scale, and gust factor with the height and time were studied. The measured thunderstorm wind spectrum and the coherence function of horizontal longitudinal reduced turbulent fluctuations were analyzed and compared with empirical models. The results showed that the wind speed profile presented an obvious “nose shape” near the peak wind speed. The longitudinal turbulence integral scale was larger than the lateral one. The Von Karman spectrum is relatively effective in fitting the thunderstorm wind spectrum. Compared with synoptic winds, the gust factor during the pass of thunderstorm wind is larger, so it seems necessary to consider the influence of thunderstorm wind in engineering design.

Characteristics and Vertical Profiles of Mean Wind and Turbulence for Typhoon, Monsoon, and Thunderstorm Winds

AbstractThe vast majority of current structural design codes and standards do not separately consider the wind and turbulence profiles for different storm types. Based on the 356-m-high Shenzhen Me...

Mean flow and turbulence characteristics of a nocturnal downburst recorded on a 213 m tall meteorological tower

AbstractThis study presents rare measurements and analysis of a nocturnal thunderstorm downburst on the 213 m tall Cabauw tower in The Netherlands. The event occurred on 12 March 2008 between 02:00 and 03:00 UTC and was measured using four ultrasonic 10-Hz anemometers positioned at 3, 60, 100, and 180 m above ground level. 1-second gusts in the outflow exceeded 30 m s−1 at 60 m and above. This wind event was accompanied by an abrupt change of wind direction from southwest to west. While the shift in wind direction corresponded with the change of upwind surface roughness, the time series of turbulence intensity and other turbulence characteristics were not affected. The statistical properties of this event were compared against the largest European database of thunderstorm winds measured in the Mediterranean. The study also demonstrated that primary and secondary vortex structures—secondary vortex being rarely observed in actual downbursts—developed at the forward edge of the cold outflow. The estimated diameter of the downdraft was 1200 m at 70 m above ground. The measured velocity profiles and friction velocity were compared against theoretical predictions of the Monin-Obukhov Similarity Theory (MOST). MOST without stratification adjustment overestimated measured friction velocity twofold. Alternative values for surface roughness during the outflow were derived based on the measured friction velocity and MOST-based fit of measured velocity profiles. Ceilometer and radar measurements were supplementary data in this analysis.

Damage to transmission towers under thunderstorm winds

AbstractA thunderstorm downburst, as defined by Fujita (1985) is “a strong downdraft which induces an outburst of damaging winds on or near the ground”. The vertical profile of wind velocities associated with downburst winds are substantially different than those corresponding to the traditional boundary layer vertical profile. In case of thunderstorms, the wind velocity does not increase with height as in the case of synoptic winds but rather maximum values are found around 50m up to 100m and thus inducing larger responses of low‐rise and mid‐rise buildings such as, for example transmission towers. These are structures of extreme ecconomic importance for any country as their damage may affect a considerable number of people. This paper presents a review of damage caused by recent thunderstorm winds to transmission towers in Romania. The date, location and intensity of thunderstorms were identified based on a vast online research of massmedia reports documenting strong wind events and associated damage between 2013 and 2017. Events that have produced partial damage or total collapse to transmission towers are described in detail. Measured wind data provided by the National Meteorological Administration from meteorological stations nearby the location of damage for each event are provided.

Using Three-Dimensional Augmented Reality to Enhance General Aviation Weather Training

This work evaluates augmented reality (AR) training materials for general aviation (GA) weather training. Reviews of GA weather training identify gaps where students lack opportunities to experience weather patterns and lack the ability to correlate weather knowledge in weather-related situations. Three-dimensional (3D) visual models may help close the gaps by visualizing information about weather processes, hazards, and visual cues. A 3D AR thunderstorm model visualizes a single-cell thunderstorm clouds, winds, precipitation, lightning, and advective movement. Preliminary evaluation of the model was conducted through a subject matter expert (SME) review and a usability study. The SME review identified improvements to the model and areas for future content design. The usability study identified usability issues with the model. Insights about the design of weather visualizations are developed into recommendations. The approach will integrate 3D AR models into the weather training curriculum to create interactive print training.

Calibration of the design wind load and snow load considering the historical climate statistics and climate change effects

In the present study, an updating of the probabilistic models used for calibrating the wind load, snow load and companion load factors for the National Building Code of Canada (NBCC) are presented. The update of probabilistic models for the extreme wind speed and ground snow depth is based on historical climatological data over Canadian sites. For the updating of the statistics of the extreme wind speed, the effect of mixed wind climate (i.e., thunderstorm winds and non-thunderstorm winds) is considered. Reliability analysis is carried out based on this update by considering different load combinations. The results indicate that, for an improved reliability consistency, the use of a high return period to specify the environmental loads and with a unit load factor is preferable to the use of 50 year return period and a load factor greater than one for structural design code making, if the coefficient of variation of the extreme climatological elements is spatially varying. Most importantly, based on these findings and the results from the climate change modelling results, sets of load scaling factors accounting for climate change effects are calibrated for different regions in Canada. Both the use of the target reliability index for a 50-year design working life as well as of the target minimum required annual reliability index within each of the 50-year design working life are considered for the reliability-based calibration. Specific recommendations on the load and companion load factors are suggested for a future edition of NBCC.

The individual and synergistic impacts of windstorms and power outages on injury ED visits in New York State

BackgroundThere is little work in assessing the impact of storm events combined with power outage (PO). In this study, we evaluated the individual and synergistic impacts of wind events and PO on overall and subtypes of injuries in New York State (NYS) and by demographics. MethodsThe emergency department (ED) visit data were obtained from the NYS Department of Health from November–April 2005–2013 to identify injury cases, length of stay and care costs. Wind event was defined according to high wind, strong wind or thunderstorm wind defined by NOAA. PO occurrence was defined when PO coverage exceeded the 50th percentile of its distribution. By comparing non-event days, we used distributed lag nonlinear models to evaluate the impacts of wind events, PO, and their combined effect on injuries during the cold season over a 0-3-day lag period, while controlling for time-varying confounders. The differences in critical care indicators between event and non-event days were also evaluated. ResultsOverall injuries ED visits (16,628,812) significantly increased during the wind events (highest Risk Ratio (RR): 1.05; 95% CI: 1.02–1.08), and were highest when wind events cooccurred with PO (highest RR: 1.14; 95% CI: 1.10–1.18), but not during PO alone (RR: 1.00; 95%CI: 0.96–1.04). The increase was also observed with all subgroups through Day 2 after the event. Greater risks exist for older adults (≥65 years) and those on Medicaid. After the joint occurrences of wind events and PO, average visits are 0.2 days longer, and cost 13% more, compared to no wind/no PO days. ConclusionThere is a significant increase in ED visits, length of stay and cost of injuries during wind events, especially when they coupled with PO and especially among older cases and Medicaid holders. Our findings may be used for planning disaster preparedness and recovery efforts.