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Paul Markowski - One of the best experts on this subject based on the ideXlab platform.
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near ground vertical vorticity in Supercell thunderstorm models
Journal of the Atmospheric Sciences, 2017Co-Authors: Richard Rotunno, Paul Markowski, George H BryanAbstract:AbstractNumerical models of Supercell thunderstorms produce near-ground rotation about a vertical axis (i.e., vertical vorticity) after the development of rain-cooled outflows and downdrafts. The physical processes involved in the production of near-ground vertical vorticity in simulated Supercells have been a subject of discussion in the literature for over 30 years. One cause for this lengthy discussion is the difficulty in applying the principles of inviscid vorticity dynamics in a continuous fluid to the viscous evolution of discrete Eulerian simulations. The present paper reports on a Lagrangian analysis of near-ground vorticity from an idealized-Supercell simulation with enhanced vertical resolution near the lower surface. The parcel that enters the low-level maximum of vertical vorticity has a history of descent during which its horizontal vorticity is considerably enhanced. In its final approach to this region, the parcel’s enhanced horizontal vorticity is tilted to produce vertical vorticity, whi...
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Comparison of the Tornadic and Nontornadic Supercells Intercepted by VORTEX2 on 10 June 2010
Monthly Weather Review, 2016Co-Authors: Alicia Klees, Paul Markowski, Yvette Richardson, Christopher C. Weiss, Joshua Wurman, Karen KosibaAbstract:AbstractOn 10 June 2010, the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) armada collected a rare set of observations of a nontornadic and a tornadic Supercell evolving in close proximity to each other. The storms and their environments were analyzed using single- and dual-Doppler radar, mobile mesonet, deployable surface mesonet, and mobile sounding data, with the goal of understanding why one Supercell produced no tornadoes while the other produced at least two. Outflow temperature deficits were similar for the two storms, both within the normal range for weakly tornadic Supercells but somewhat cold relative to significantly tornadic Supercells. The storms formed in a complex environment, with slightly higher storm-relative helicity near the tornadic Supercell. The environment evolved significantly in time, with large thermodynamic changes and increases in storm-relative helicity, leading to conditions much more favorable for tornadogenesis. After a few hours, a new s...
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the influence of environmental low level shear and cold pools on tornadogenesis insights from idealized simulations
Journal of the Atmospheric Sciences, 2014Co-Authors: Paul Markowski, Yvette RichardsonAbstract:AbstractIdealized, dry simulations are used to investigate the roles of environmental vertical wind shear and baroclinic vorticity generation in the development of near-surface vortices in Supercell-like “pseudostorms.” A cyclonically rotating updraft is produced by a stationary, cylindrical heat source imposed within a horizontally homogeneous environment containing streamwise vorticity. Once a nearly steady state is achieved, a heat sink, which emulates the effects of latent cooling associated with precipitation, is activated on the northeastern flank of the updraft at low levels. Cool outflow emanating from the heat sink spreads beneath the updraft and leads to the development of near-surface vertical vorticity via the “baroclinic mechanism,” as has been diagnosed or inferred in actual Supercells that have been simulated and observed.An intense cyclonic vortex forms in the simulations in which the environmental low-level wind shear is strong and the heat sink is of intermediate strength relative to the...
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the pretornadic phase of the goshen county wyoming Supercell of 5 june 2009 intercepted by vortex2 part i evolution of kinematic and surface thermodynamic fields
Monthly Weather Review, 2012Co-Authors: Paul Markowski, Erik N. Rasmussen, Yvette Richardson, Joshua Wurman, Karen Kosiba, James Marquis, Paul Robinson, David C Dowell, Robert DaviesjonesAbstract:AbstractThe authors analyze the pretornadic phase (2100–2148 UTC; tornadogenesis began at 2152 UTC) of the Goshen County, Wyoming, Supercell of 5 June 2009 intercepted by the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2). The analysis relies on radar data from the Weather Surveillance Radar-1988 Doppler (WSR-88D) in Cheyenne, Wyoming (KCYS), and a pair of Doppler-on-Wheels (DOW) radars, mobile mesonet observations, and mobile sounding observations.The storm resembles Supercells that have been observed in the past. For example, it develops a couplet of counter-rotating vortices that straddle the hook echo within the rear-flank outflow and are joined by arching vortex lines, with the cyclonic vortex becoming increasingly dominant in the time leading up to tornadogenesis. The outflow in the hook echo region, where sampled, has relatively small virtual potential temperature θυ deficits during this stage of evolution. A few kilometers upstream (north) of the location of maxim...
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descending reflectivity cores in Supercell thunderstorms observed by mobile radars and in a high resolution numerical simulation
Weather and Forecasting, 2009Co-Authors: Zack Byko, Paul Markowski, Yvette Richardson, Josh Wurman, Edwin AdlermanAbstract:Abstract This paper is motivated by the recent interest in the “descending reflectivity cores” (DRCs) that have been observed in some Supercell thunderstorms prior to the development or intensification of low-level rotation. The DRCs of interest descend on the right rear flank of the storms and are small in scale, relative to the main radar echo. They are observed to descend from the echo overhang and, upon reaching low levels, have been found to contribute to the formation or evolution of hook echoes, which are perhaps the most familiar radar characteristic of Supercells. Herein, observations of DRCs obtained by a mobile Doppler radar at close range are presented. The data afford higher-resolution views of DRCs and their accompanying radial velocity fields than typically are available from operational radars, although one drawback is that some of the larger-scale perspective is sacrificed (e.g., the origin of the DRC and its possible connection to the reflectivity near the updraft summit are within the c...
Matthew J. Bunkers - One of the best experts on this subject based on the ideXlab platform.
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Observations of Right-Moving Supercell Motion Forecast Errors
Weather and Forecasting, 2018Co-Authors: Matthew J. BunkersAbstract:AbstractTwo shear-based Supercell motion forecast methods are assessed to understand how each method performs under differing environmental conditions for observed right-moving Supercells. Accordingly, a 573-case observational dataset is partitioned into small versus large values of environmental and storm-related variables such as bulk wind shear, convective available potential energy, mean wind, storm motion, and storm-relative helicity (SRH). In addition, hodographs are partitioned based on the tornado damage scale, as well as where the storm motion falls among the four quadrants. With respect to the 573-case dataset, the largest Supercell motion forecast errors generally occur when the (i) observed midlevel (4–5 km AGL) storm-relative winds are either anomalously weak or strong, (ii) observed 0–3-km AGL SRH is large, (iii) Supercell motion is fast, (iv) convective inhibition is strong, or (v) the surface–500-mb (1 mb = 1 hPa) RH is low. Moreover, significantly tornadic Supercells are biased 1.2 m s−1 ...
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Choosing a Universal Mean Wind for Supercell Motion Prediction
Journal of Operational Meteorology, 2014Co-Authors: Matthew J. Bunkers, Roger Edwards, Richard L. Thompson, David A. Barber, Jonathan GarnerAbstract:The 06-km AGL mean wind has been used widely in operations to predict Supercell motion. However, when a Supercell is low-topped or elevated, its motion may be poorly predicted with this default mean wind— which itself could be height-based or pressure-weighted. This information suggests that a single, fixed layer is inappropriate for some situations, and thus various mean-wind parameters are explored herein. A dataset of 583 observed and 829 Rapid Update Cycle Supercell soundings was assembled. When the mean wind is computed using pressure weighting for an effective inflow-layer as the base, and 65% of the most-unstable equilibrium level height as the top, the result is that better Supercell motion predictions can be obtained for low-topped and elevated Supercells. Such a mean-wind modification would come at the cost of only a minor increase in mean absolute error for the entire sample of Supercell cases considered.
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Documentation of a Rare Tornadic Left-Moving Supercell
E-Journal of Severe Storms Meteorology, 2007Co-Authors: Matthew J. Bunkers, John W. StoppkotteAbstract:An F1 anticyclonic tornado (i.e., clockwise rotation in the Northern Hemisphere) was produced by an intense left-moving/anticyclonic Supercell near Rushville, Nebraska, on 20 June 2006. This is only the fifth formally documented left-moving Supercell that produced an anticyclonic tornado. The left-moving Supercell exhibited an impressive hook echo, mesoanticyclone, and bounded weak-echo region at the time of tornado occurrence—rivaling those of its right-moving counterparts. Since tornadic left-moving Supercells are extremely rare, and thus potentially difficult to recognize, this paper serves to document the radar characteristics and environmental conditions of this event.
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An Observational Examination of Long-Lived Supercells. Part II: Environmental Conditions and Forecasting
Weather and Forecasting, 2006Co-Authors: Matthew J. Bunkers, Brian A. Klimowski, Jeffrey S. Johnson, Lee J. Czepyha, Jason M. Grzywacz, Mark R. HjelmfeltAbstract:Abstract The local and larger-scale environments of 184 long-lived Supercell events (containing one or more Supercells with lifetimes ≥4 h; see Part I of this paper) are investigated and subsequently compared with those from 137 moderate-lived events (average Supercell lifetime 2–4 h) and 119 short-lived events (average Supercell lifetime ≤2 h) to better anticipate Supercell longevity in the operational setting. Consistent with many previous studies, long-lived Supercells occur in environments with much stronger 0–8-km bulk wind shear than what is observed for short-lived Supercells; this strong shear leads to significant storm-relative winds in the mid- to upper levels for the longest-lived Supercells. Additionally, the bulk Richardson number falls into a relatively narrow range for the longest-lived Supercells—ranging mostly from 5 to 45. The mesoscale to synoptic-scale environment can also predispose a Supercell to be long or short lived, somewhat independent of the local environment. For example, long...
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An Observational Examination of Long-Lived Supercells. Part I: Characteristics, Evolution, and Demise
Weather and Forecasting, 2006Co-Authors: Matthew J. Bunkers, Mark R. Hjelmfelt, Paul L. SmithAbstract:Observations of Supercells and their longevity across the central and eastern United States are examined, with the primary focus on understanding the properties of long-lived Supercells (defined as Supercells lasting 4 h). A total of 224 long-lived Supercells, occurring in 184 separate events, are investigated. These properties are compared with those of short-lived Supercells (lifetimes 2 h) to determine the salient differences between the two classifications. A key finding is that long-lived Supercells are considerably more isolated and discrete than short-lived Supercells; as a result, the demise of a long-lived Supercell (i.e., the end of the Supercell phase) is often signaled by a weakening of the storm’s circulation and/or a rapid dissipation of the thunderstorm. In contrast, short-lived Supercells commonly experience a demise linked to storm mergers and convective transitions (e.g., evolution to a bow echo). Also noteworthy, 36% of the long-lived Supercell events were associated with strong or violent tornadoes (F2–F5), compared with only 8% for the short-lived Supercell events. Evolutionary characteristics of long-lived Supercells vary geographically across the United States, with the largest contrasts between the north-central United States and the Southeast. For example, 86% of the long-lived Supercells across the north-central United States were isolated for most of their lifetime, whereas only 35% of those in the Southeast displayed this characteristic. Not surprisingly, the convective mode was discrete for 70% of the long-lived Supercell events across the north-central United States, compared with 39% for the Southeast.
Matthew D. Parker - One of the best experts on this subject based on the ideXlab platform.
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Simulated Supercells in Nontornadic and Tornadic VORTEX2 Environments
Monthly Weather Review, 2016Co-Authors: Brice E. Coffer, Matthew D. ParkerAbstract:AbstractThe composite near-storm environments of nontornadic and tornadic Supercells sampled during the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) both appear to be generally favorable for Supercells and tornadoes. It has not been clear whether small differences between the two environments (e.g., more streamwise horizontal vorticity in the lowest few hundred meters above the ground in the tornadic composite) are actually determinative of storms’ tornadic potential. From the VORTEX2 composite environments, simulations of a nontornadic and a tornadic Supercell are used to investigate storm-scale differences that ultimately favor tornadogenesis or tornadogenesis failure. Both environments produce strong Supercells with robust midlevel mesocyclones and hook echoes, though the tornadic Supercell has a more intense low-level updraft and develops a tornado-like vortex exceeding the EF3 wind speed threshold. In contrast, the nontornadic Supercell only produces shallow vortic...
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Composite VORTEX2 Supercell Environments from Near-Storm Soundings
Monthly Weather Review, 2014Co-Authors: Matthew D. ParkerAbstract:AbstractThree-dimensional composite analyses using 134 soundings from the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) reveal the nature of near-storm variability in the environments of Supercell thunderstorms. Based upon the full analysis, it appears that vertical wind shear increases as one approaches a Supercell within the inflow sector, providing favorable conditions for Supercell maintenance (and possibly tornado formation) despite small amounts of low-level cooling near the storm. The seven analyzed tornadic Supercells have a composite environment that is clearly more impressive (in terms of widely used metrics) than that of the five analyzed nontornadic Supercells, including more convective available potential energy (CAPE), more vertical wind shear, higher boundary layer relative humidity, and lower tropospheric horizontal vorticity that is more streamwise in the near-storm inflow. The widely used Supercell composite parameter (SCP) and significant tornado param...
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A numerical investigation of Supercells in landfalling tropical cyclones
Geophysical Research Letters, 2011Co-Authors: M. J. Morin, Matthew D. ParkerAbstract:[1] Supercell thunderstorms are known to occur in the outer rainbands of tropical cyclones (TCs), and these cells are of interest because they are occasionally tornadic. A series of multi-scale quasi-idealized TC simulations are used to study the development of outer rainband Supercells. Within the environment of landfalling TCs, the sea-to-land transition of the rainbands is found to locally benefit Supercell development onshore due in part to (1) enhanced surface-based destabilization during the day and (2) increased surface friction slowing and backing the low-level winds. Landfall time of day is shown to have a substantial impact on the average number, strength, and lifetime of the ensemble of simulated Supercells. These idealized simulations represent a first attempt at controlled hypothesis tests for Supercell and tornado ingredients within the context of a highly resolved parent TC.
Morris L. Weisman - One of the best experts on this subject based on the ideXlab platform.
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Predicting Supercell Motion Using a New Hodograph Technique
Weather and Forecasting, 2000Co-Authors: Matthew J. Bunkers, Brian A. Klimowski, Jon W. Zeitler, Richard L. Thompson, Morris L. WeismanAbstract:A physically based, shear-relative, and Galilean invariant method for predicting Supercell motion using a hodograph is presented. It is founded on numerous observational and modeling studies since the 1940s, which suggest a consistent pattern to Supercell motion exists. Two components are assumed to be largely responsible for Supercell motion: (i) advection of the storm by a representative mean wind, and (ii) propagation away from the mean wind either toward the right or toward the left of the vertical wind shear—due to internal Supercell dynamics. Using 290 Supercell hodographs, this new method is shown to be statistically superior to existing methods in predicting Supercell motion for both right- and left-moving storms. Other external factors such as interaction with atmospheric boundaries and orography can have a pronounced effect on Supercell motion, but these are difficult to quantify prior to storm development using only a hodograph.
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The Interaction of Numerically Simulated Supercells Initiated along Lines
Monthly Weather Review, 2000Co-Authors: Howard B. Bluestein, Morris L. WeismanAbstract:Abstract Supercells in the southern plains are often localized, forming as cells along a convective line, even though the environment may support Supercell formation over a much broader, mesoscale region. A set of numerical experiments is devised in which it is demonstrated that the evolution of Supercells in a homogeneous environment depends upon the orientation of the vertical-shear profile with respect to the orientation of the line along which convection is initiated (the “line of forcing”). This work is motivated by the observations that the nature and consequences of the interaction of neighboring cells depend upon differential cell motion, which in turn is a function of the characteristics and orientation of the vertical-shear profile and its impact on the behavior of outflow boundaries. Results for various orientations of the vertical-shear vector with respect to the line along which cells are initiated are described and interpreted physically. It is found that in idealized numerical simulations, ...
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Simulations of shallow Supercell storms in landfalling hurricane environments
Monthly Weather Review, 1996Co-Authors: Eugene W. Mccaul, Morris L. WeismanAbstract:Abstract Numerical simulations of the convective storms that form in tornado-producing landfalling hurricanes show that shallow Supercells are possible, even though buoyancy is limited because ambient lapse rates are close to moist adiabatic. Updrafts generally reach peak intensity at low levels, often around 2 km above the surface. By comparison, a simulated midlatitude Supercell typical of the Great Plains of the United States exhibits a pronounced increase in storm size, both horizontally and vertically. At low levels, however, the hurricane-spawned storms may contain updrafts that rival or exceed in intensity those of Great Plains Supercells at similar levels. Simulations made using a tornado-proximity sounding from the remnants of Hurricane Danny in 1985 produce a small but intense Supercell, a finding consistent with the available observational evidence. Although the amplitude of parcel buoyancy is often small in hurricane environments, its concentration in the strongly sheared lower troposphere pro...
Louis J. Wicker - One of the best experts on this subject based on the ideXlab platform.
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The Influence of Midtropospheric Dryness on Supercell Morphology and Evolution
Monthly Weather Review, 1998Co-Authors: Matthew S. Gilmore, Louis J. WickerAbstract:Abstract This work studies the relationship between midtropospheric dryness and Supercell thunderstorm morphology and evolution using a three-dimensional, nonhydrostatic cloud model. Environments that differ only in midtropospheric dryness are found to produce Supercells having different low-level outflow and rotational characteristics. Thunderstorms forming in environments with moderate vertical wind shear, large instability, and very dry midtropospheric air produce strong low-level outflow. When this low-level outflow propagates faster than the midlevel mesocyclone, the storm updraft and low-level mesocyclone weaken. However, in environments with larger vertical wind shear or with higher-altitude dry midtropospheric air, the low-level outflow is not as detrimental to the Supercell. This provides a possible explanation for why some environments that appear favorable for the development of strong low-level mesocyclones in Supercells fail to do so. Downdraft convective available potential energy (DCAPE) is...
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simulation and analysis of tornado development and decay within a three dimensional Supercell thunderstorm
Journal of the Atmospheric Sciences, 1995Co-Authors: Louis J. Wicker, R. B. WilhelmsonAbstract:Abstract A three-dimensional numerical simulation using a two-way interactive nested grid is to study tornado-genesis within a Supercell. During a 40-minute period, two tornadoes grow and decay within the storm's mesocyclone. The tornadoes have life spans of approximately 10 minutes. Maximum ground-relative surface wind speeds exceed 60 m s−1 during both tornadoes, and horizontal pressure gradients reach 18 hPa km−1 during the second tornado. Comparison of the simulated storm evolution with Doppler and field observations of Supercells and tornadoes shows many similar features. Vertical vorticity in the mesocyclone and the tornado vortex at low levels is initially created by the tilting of the environmental vorticity and baroclinically generated vorticity along the forward gland gust front of the storm. Tornadogenesis is initiated when mesocyclone rotation increase above cloud base. The increased rotation generates lower pressure in the mesocyclone, increasing the upward pressure gradient forces. The upwar...
