Observations of a Storm Containing Misocyclones, Downbursts, and Horizontal Vortex Circulations

Kessinger, Cathy; Parsons, David B.; Wilson, James W.

doi:10.1175/1520-0493(1988)116<1959:ooascm>2.0.co;2

Cited by 29 publications

(16 citation statements)

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“…On the other hand, radar observations showed a number of features that might suggest the mini-supercell character of some of the convective structures observed. A possible misoanticyclone could be associated with downdrafts as observed in previous studies of multicell (Kessinger et al, 1988) or supercell storms (Brown and Knupp, 1980;Bluestein et al, 1997;Monteverdi et al, 2001). The strong low-level jet observed and the associated intense vertical shear and horizontal vorticity is a feature compatible both with non-supercell and mini-supercell characteristics of the storms.…”

Section: Summary and Discussionmentioning

confidence: 95%

An observational study of the 7 September 2005 Barcelona tornado outbreak

Bech¹,

Pascual

Rigo³

et al. 2007

Nat. Hazards Earth Syst. Sci.

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Abstract. This paper presents an observational study of the tornado outbreak that took place on the 7 September 2005 in the Llobregat delta river, affecting a densely populated and urbanised area and the Barcelona International airport (NE Spain). The site survey confirmed at least five short-lived tornadoes. Four of them were weak (F0, F1) and the other one was significant (F2 on the Fujita scale). They started mostly as waterspouts and moved later inland causing extensive damage estimated in 9 million Euros, three injured people but fortunately no fatalities. Large scale forcing was provided by upper level diffluence and low level warm air advection. Satellite and weather radar images revealed the development of the cells that spawned the waterspouts along a mesoscale convergence line in a highly sheared and relatively low buoyant environment. Further analysis indicated characteristics that could be attributed indistinctively to nonsupercell or to mini-supercell thunderstorms.

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Section: Summary and Discussionmentioning

confidence: 95%

An observational study of the 7 September 2005 Barcelona tornado outbreak

Bech¹,

Pascual

Rigo³

et al. 2007

Nat. Hazards Earth Syst. Sci.

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“…These analytical models for downbursts are extremely efficient and are widely applied in wind engineering research for buildings [15], in aviation-related studies [16,17], and in the assessment of turbine loads. Even though these analytical models for the mean wind field and associated turbulence fields are an improvement over the current IEC guidelines, the models are deficient in accurately capturing several physical aspects of the downburst wind fields such as the formation of surface ring vortices [1,[18][19][20], spatially coherent structures at the leading edge of a moving downburst [21,22], and accurate representations of the generated turbulence. In recent years, the modeling of downburst wind fields with the help of large-eddy simulation (LES) has gained in interest.…”

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confidence: 99%

On Wind Turbine Loads During Thunderstorm Downbursts in Contrasting Atmospheric Stability Regimes

Hawbecker

Basu

et al. 2019

Energies

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Severe winds produced by thunderstorm downbursts pose a serious risk to the structural integrity of wind turbines. However, guidelines for wind turbine design (such as the International Electrotechnical Commission Standard, IEC 61400-1) do not describe the key physical characteristics of such events realistically. In this study, a large-eddy simulation model is employed to generate several idealized downburst events during contrasting atmospheric stability conditions that range from convective through neutral to stable. Wind and turbulence fields generated from this dataset are then used as inflow for a 5-MW land-based wind turbine model; associated turbine loads are estimated and compared for the different inflow conditions. We first discuss time-varying characteristics of the turbine-scale flow fields during the downbursts; next, we investigate the relationship between the velocity time series and turbine loads as well as the influence and effectiveness of turbine control systems (for blade pitch and nacelle yaw). Finally, a statistical analysis is conducted to assess the distinct influences of the contrasting stability regimes on extreme and fatigue loads on the wind turbine.Energies 2019, 12, 2773 2 of 30 duration, with stochastically generated turbulence added on to a mean flow field. From the IEC standard, the extreme operating gust (EOG) is defined as:where U(z, t) represents the wind speed as a function of height, z, and time, t; U(z) is a power-law wind profile; U gust is the gust magnitude at hub height; and T is a specific time span for the gust function, taken to be 10.5 s. These mean wind fields derived from the analytical functions can be grossly different from what has been observed during downbursts [7]; they also may not accurately describe the strong vertical shear observed sometimes, and the associated non-stationary characteristics of the flow field. As well, the turbulence models employed are often for overly simplified cases with assumptions of near-neutral stability conditions that may not be justified. Due to these shortcomings, a series of earlier studies [8][9][10][11][12][13] were conducted to assess how downburst-related inflow fields (based on observational data but analytically derived [14]) could influence turbine loads. These studies highlighted the potential impacts of downbursts on a single wind turbine as well as on an entire wind farm or turbine array. They also emphasized the importance of improved models over the current IEC guidelines suggested for such events, when considering turbine design and control. In comparison with the turbine loads resulting from the IEC load cases for extreme coherent gust (ECG), extreme direction change (EDC), and extreme coherent gust with direction change (ECD), all believed to represent transient events such as downbursts, the turbine loads that were produced when driven by the data-based analytical models differed greatly. (In two cases, as found by Nguyen et al. [8], the analytical models predicted loads that were 86% larger than those based...

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“…Most occurred with isolated pulse storms though some occurred in conjunction with multicellular convective lines. Kessinger et al (1988) and Roberts and Wilson (1989) discussed factors that result in a variety of Doppler velocity features associated with downbursts that may be used as predictors. This environment supports the development of low-reflectivity microbursts (LRMs) where very little rain reaches the surface and downdrafts are driven primarily by evaporative cooling as small raindrops and graupel fall from a relatively high cloud base into dry subcloud air (Srivastava 1985).…”

Section: Downburst Backgroundmentioning

confidence: 99%

“…The typical local thermodynamic environment for JAWS microbursts is characterized by a deep, dry, well-mixed boundary layer capped by a layer of high relative humidity (RH) with low convective available potential energy (CAPE). Rotation can initially be separate from a Hjelmfelt (1988) and Kessinger et al (1988) discussed how rotors along the leading edge of an outflow are associated with the strongest winds. Roberts and Wilson (1989) reported on a spectrum of microbursts and their association with various reflectivity values that includes the categories moderate-reflectivity microbursts (MRMs) and high-reflectivity microbursts (HRMs).…”

Section: Downburst Backgroundmentioning

confidence: 99%

“…Similar differences between the KIWA and SR1 data were noted aloft. Hjelmfelt (1988) and Kessinger et al (1988) pointed out that rotors along the leading edge of a microburst can result in a local enhancement of winds as well as very small-scale convergence-divergence couplets. The rotational features were likely the result of the inferred downdraft as noted by Rinehart et al (1995).…”

Section: Radar Data Analysismentioning

confidence: 99%

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Investigation of a Severe Downburst Storm near Phoenix, Arizona, as Seen by a Mobile Doppler Radar and the KIWA WSR-88D

Vasiloff

Howard

2009

Weather and Forecasting

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A Shared Mobile Atmospheric Research and Teaching Radar (SMART-R) was deployed near Phoenix, Arizona, during the summer of 2004. The goal was to capture a severe microburst at close range to understand the low-altitude wind structure and evolution. During the evening of 27 July, a severe storm formed along the Estrella Mountains south of Phoenix and moved south of the SMART-R as well as the National Weather Service's (NWS) Weather Surveillance Radar-1988 Doppler (WSR-88D) in Phoenix (KIWA). Several microburst-downburst pulses were observed by radar and a surface wind gust of 67 mi h 21 was reported. The radar data illustrate the finescale structure of the microburst pulses, with the SMART-R's higher-resolution data showing Doppler velocities 3-4 m s 21 greater than the KIWA radar. SMART-R wind shear values were 2-3 times greater with the finer resolution of the SMART-R revealing smaller features in the surface outflow wind structure. Asymmetric outflow may have been a factor as well in the different divergence values. The evolution of the outflow was very rapid with the 5-min KIWA scan intervals being too course to sample the detailed evolution. The SMART-R scans were at 3-5-min intervals and also had difficulty resolving the event. The storm environment displayed characteristics of both moderate-to-highreflectivity microbursts, typical of the high plains of Colorado.

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Observations of a Storm Containing Misocyclones, Downbursts, and Horizontal Vortex Circulations

Cited by 29 publications

References 0 publications

An observational study of the 7 September 2005 Barcelona tornado outbreak

An observational study of the 7 September 2005 Barcelona tornado outbreak

On Wind Turbine Loads During Thunderstorm Downbursts in Contrasting Atmospheric Stability Regimes

Investigation of a Severe Downburst Storm near Phoenix, Arizona, as Seen by a Mobile Doppler Radar and the KIWA WSR-88D

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