More Like this

1. CFD model validation with experimental tornado wind field & comparison of wind field in different tornado chambers

   https://doi.org/https://doi.org/10.12989/was.2021.33.5.367  

   Verma, Sumit.; Selvam, Rathinam P. (January 2021, Wind and Structures)

   Validation of CFD tornado wind field with experimental or field measurements is limited to comparison of tangential velocity profile at certain elevations above the ground level and few studies are based on comparison of pressure profile. However, important tornado vortex features such as touchdown swirl ratio (ST), core radius (rc), maximum tangential velocity (Vtmax), elevation of maximum tangential velocity (zc) and pressure distribution over a range of varying swirl ratios which strongly influences tornado forces on a building have not been accounted for validation of tornado wind field. In this study, important tornado vortex features are identified and validated with experimental measurements; the important tornado features obtained from the CFD model are found to be in reasonable agreement with experimental measurements. Besides, tornado chambers with different geometrical features (such as different outlet size and location and total heights) are used in different works of literature; however, the effect of variation of those key geometrical features on tornado wind field is not very well understood yet. So, in this work, the size of outlet and total height are systematically varied to study the effect on important tornado vortex parameters. Results indicate that reducing outlet diameter in a tornado chamber increases ST, Vtmax and zc and decreases rc. Similarly, increasing total height of tornado chamber decreases ST, Vtmax and rc whereas zc remains nearly constant. Overall, it is found that variation of outlet diameter has a stronger effect on tornado wind field than the variation in total height of tornado chamber. 

   more » « less
2. Analytical Approach to Characterize Tornado-Induced Loads on Lattice Structures

   https://doi.org/10.1061/(ASCE)ST.1943-541X.0002660  

   Alipour, A.; Sarkar, PP.; Dikshit, S.; Razavi, A.; Jafari, M. (June 2020, Journal of structural engineering)

   This paper presents a quasi-steady technique that combines aerodynamic force coefficients from straight-line wind tunnel tests with empirically developed tornado wind speed profiles to estimate the time history of aerodynamic loads on lattice structures. The methodology is specifically useful for large and geometrically complex structures that could not be modeled with reasonable scales in the limited number of tornado simulation facilities across the world. For this purpose, the experimentally developed tornado wind speed profiles were extracted from a laboratory tornado wind field and aerodynamic force coefficients of different segments of a lattice tower structure were assessed for various wind directions in a wind tunnel. The proposed method was then used to calculate the wind forces in the time domain on the model lattice tower for different orientation angles with respect to the tornado’s mean path based on the empirical tornado wind speed profiles and the measured aerodynamic force coefficient of each tower segment, where the wind field at the tower location was updated at each time step as the tornado went past the tower. A tornado laboratory simulation test was conducted to measure the wind loads on a scaled model of a lattice tower subject to a translating tornado for the purpose of validation of the proposed method. The moving average of the horizontal wind force on the lattice tower model that was calculated with this method compared very well with that measured in a laboratory tornado simulator, which paves the way for the use of straight-line wind tunnels to assess tornado-induced loads on a lattice structure and possibly other similar structures. 

   more » « less
3. Examining the Relationship between Tropopause Polar Vortices and Tornado Outbreaks

   https://doi.org/10.1175/WAF-D-21-0058.1  

   Bray, Matthew T.; Cavallo, Steven M.; Bluestein, Howard B. (August 2021, Weather and Forecasting)

   null (Ed.)

   Abstract Mid-latitude jet streaks are known to produce conditions broadly supportive of tornado outbreaks, including forcing for large-scale ascent, increased wind shear, and decreased static stability. Although many processes may initiate a jet streak, we focus here on the development of jet maxima by interactions between the polar jet and tropopause polar vortices (TPVs). Originating from the Arctic, TPVs are long-lived circulations on the tropopause, which can be advected into the mid-latitudes. We hypothesize that when these vortices interact with the jet, they may contribute supplemental forcing for ascent and shear to tornado outbreaks, assuming other environmental conditions supportive of tornado development exist. Using a case set of significant tornado outbreak days from three states—Oklahoma, Illinois, and Alabama—we show that a vortex-jet streak structure is present (within 1250 km) in around two-thirds of tornado outbreaks. These vortices are commonly Arctic in origin (i.e., are TPVs) and are advected through a consistent path of entry into the mid-latitudes in the week before the outbreak, moving across the Northern Pacific and into the Gulf of Alaska before turning equatorward along the North American coast. These vortices are shown to be more intense and longer-lived than average. We further demonstrate that statistically significant patterns of wind shear, quasi-geostrophic forcing for ascent, and low static stability are present over the outbreak regions on the synoptic scale. In addition, we find that TPVs associated with tornadic events occur most often in the spring and are associated with greater low-level moisture when compared to non-tornadic TPV cases. 

   more » « less
4. Using Deep Learning and Advanced Image Processing for the Automated Estimation of Tornado-Induced Treefall

   https://doi.org/10.3390/rs16071130  

   Nasimi, Mitra; Wood, Richard L (April 2024, Remote Sensing)

   Liu, Weifeng (Ed.)

   Each year, numerous tornadoes occur in forested regions of the United States. Due to the substantial number of fallen trees and accessibility issues, many of these tornadoes remain poorly documented and evaluated. The process of documenting tree damage to assess tornado intensity is known as the treefall method, an established and reliable technique for estimating near-surface wind speed. Consequently, the demand for documenting fallen trees has increased in recent years. However, the treefall method proves to be extremely expensive and time-consuming, requiring a laborious assessment of each treefall instance. This research proposes a novel approach to evaluating treefall in large, forested regions using deep learning-based automated detection and advanced image processing techniques. The developed treefall method relies on high-resolution aerial imagery from a damaged forest and involves three main steps: (1) instance segmentation detection, (2) estimating tree taper and predicting fallen tree directions, and (3) obtaining subsampled treefall vector results indicating the predominant flow direction in geospatial coordinates. To demonstrate the method’s effectiveness, the algorithm was applied to a tornado track rated EF-4, which occurred on 10 December 2021, cutting through the Land Between the Lakes National Recreation Area in Kentucky. Upon observation of the predicted results, the model is demonstrated to accurately predict the predominant treefall angles. This deep-learning-based treefall algorithm has the potential to speed up data processing and facilitate the application of treefall methods in tornado evaluation. 

   more » « less
5. Using Ensemble Sensitivity Analysis to Identify Storm Characteristics Associated with Tornadogenesis in High-Resolution Simulated Supercells

   https://doi.org/10.1175/MWR-D-22-0288.1  

   Hutson, Abby; Weiss, Christopher (October 2023, Monthly Weather Review)

   Abstract This study aims to objectively identify storm-scale characteristics associated with tornado-like vortex (TLV) formation in an ensemble of high-resolution supercell simulations. An ensemble of 51 supercells is created using Cloud Model version 1 (CM1). The first member is initialized using a base state populated by the Rapid Update Cycle (RUC) proximity sounding near El Reno, Oklahoma, on 24 May 2011. The other 50 ensemble members are created by randomly perturbing the base state after a supercell has formed. There is considerable spread between ensemble members, with some supercells producing strong, long-lived TLVs, while others do not produce a TLV at all. The ensemble is analyzed using the ensemble sensitivity analysis (ESA) technique, uncovering storm-scale characteristics that are dynamically relevant to TLV formation. In the rear flank, divergence at the surface southeast of the TLV helps converge and contract existing vertical vorticity, but there is no meaningful sensitivity to rear-flank outflow temperature. In the forward flank, warm temperatures within the cold pool are important to TLV production and magnitude. The longitudinal positioning of strong streamwise vorticity is also a clear indicator of TLV formation and strength, especially within 5 min of when the TLV is measured. Significance StatementTornadoes that form in supercell thunderstorms (long-lived storms with a rotating updraft) are heavily influenced by the features created by the storm itself, such as the temperature of a downdraft. In this study, many different iterations of a strong supercell thunderstorm are simulated, in which tornado-like features are formed at different times with widely different strengths. A statistical method is used to identify what the storms had in common when they produced a tornado-like feature, and what they had in common when one failed to form. This study is important because it highlights which storm features are most influential to tornado formation using an objective method, with results that can be used when observing supercells in the field. 

   more » « less