The Influence of a Local Swirl Ratio on Tornado Intensification near the Surface

Lewellen, D. C.; Lewellen, W. S.; Xia, Jianjun

doi:10.1175/1520-0469(2000)057<0527:tioals>2.0.co;2

Cited by 167 publications

(166 citation statements)

References 15 publications

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“…This method has been used in both two-and three-dimensional models by Fiedler (1993, 1998), Trapp and Fiedler (1995, and Trapp and Davies-Jones (1997) so that a much larger domain could be used while still resolving the boundary layer. Both domain restriction and grid stretching have been used by W. Lewellen et al (1997) and D. Lewellen et al (2000) in their Large-Eddy-Simulations of the corner region.…”

Section: Numerical Modelling Of Tornado-like Vortices and The Use Of mentioning

confidence: 99%

“…Such domain restriction, by construction, decouples the vortex from the surrounding environment, and must assume predetermined properties for the inflow and outflow of the corner region. As Lewellen et al (2000) showed in some detail, changes in the inflow and outflow boundary conditions have significant impacts on the near-surface vortex structure. Similar conclusions were found by Smith (1987) and Fiedler (1995).…”

Section: Numerical Modelling Of Tornado-like Vortices and The Use Of mentioning

confidence: 99%

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Studies of the relationship between environmental forcing and the structure and dynamics of tornado-like vortices

Nolan¹,

Almgren²,

Bell³

2000

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Axisymmetric numerical simulations continue to provide insight into how the structure, dynamics, and maximum windspeeds of tornadoes, and other convectively-maintained vortices, are influenced by the surrounding environment. This work is continued with a new numerical model of axisymmetric incompresible flow that incorporates adaptive mesh refinement. The model dynamically increases or decreases the resolution in regions of interest as determined by a specified refinement criterion. Here, the criterion used is based on the cell Reynolds number , so that the flow is guaranteed to be laminar on the scale of the local grid spacing.The model is used to investigate how the altitude and shape of the convective forcing, the size of the domain, and the effective Reynolds number (based on the choice of the eddy viscosity ν) influence the structure and dynamics of the vortex. Over a wide variety of domain and forcing geometries, the vortex Reynolds number Γ/ν (the ratio of the far-field circulation to the eddy viscosity) is shown to be the most important parameter for determining vortex structure and behavior. Furthermore, it is found that the vertical scale of the convective forcing only affects the vortex inasmuch as this vertical scale contributes to the total strength of the convective forcing. The horizontal scale of the convective forcing, however, is found to be the fundamental length scale in the problem, in that it can determine both the circulation of the fluid that is drawn into the vortex core, and also influences the depth of the swirling boundary layer. Higher mean windspeeds are sustained as the eddy viscosity is decreased; however, it is observed that the highest windspeeds are found in the high-swirl, two-celled vortex regime rather than in the low-swirl, one-celled regime, which is contrast with some previous results.

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Section: Numerical Modelling Of Tornado-like Vortices and The Use Of mentioning

confidence: 99%

Section: Numerical Modelling Of Tornado-like Vortices and The Use Of mentioning

confidence: 99%

Studies of the relationship between environmental forcing and the structure and dynamics of tornado-like vortices

Nolan¹,

Almgren²,

Bell³

2000

View full text Add to dashboard Cite

show abstract

“…The tangential velocity drops to zero at the surface due to surface friction (Lewellen et al, 2000). The surface friction effect results in the vertical distribution of the near-surface tangential velocity on the domain boundary (Leslie and Smith, 1977;Vatistas, Kozel and Mih, 1991).…”

Section: Horizontal Vorticity and Surface Frictionmentioning

confidence: 99%

“…Instead of considering the larger scale, Lewellen et al (2000) takes into account a larger domain than might seem necessary in their simulation of the air flow of tornados. In this way, a physically reasonable range of flow fields immediately bounding the corner flow domain is obtained by imposing a variety of flows on the outer tornado scale as the far-field boundary conditions.…”

Section: Introductionmentioning

confidence: 99%

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An Overview of Surface Conditions in Numerical Simulations of Dust Devils and the Consequent Near-surface Air Flow Fields

Wei

Zhao

2010

Aerosol Air Qual. Res.

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Dust devils are generally attributed to the near-surface conditions, usually the composite actions of the surface parameters, such as heat flux, wind shear and surface friction. Dust devil scale (DD-scale) numerical modeling has been developed to simulate the air flow of dust devils (Gu et al., 2006(Gu et al., , 2008. In the DD-scale model, local vorticity is imposed on the boundary domain (the outer dust devil), as described by Lewellen et al. (2000). The computational domain is close to the size of convective plumes. The predicted physical parameters of Arizona-type dust devil, such as the maximum tangential velocity, the updraft velocity, the pressure drop in the inner core region and even the inverse flow at the top of the core region, approach the observation results, testifying the validity of the DD-scale modeling. The effects of buoyancy (ground temperature) and surface friction (surface momentum impact height) on the fine scale structure of dust devils are further examined in this paper. The results indicate that even with small temperature difference (weak buoyancy), severe dust devils may be formed by strong local vorticity, and that different surface momentum impact heights may result in different conic angles of corner flow.

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Analysis of the horizontal two‐dimensional near‐surface structure of a winter tornadic vortex using high‐resolution in situ wind and pressure measurements

Kato

Kusunoki²,

Satô³

et al. 2015

JGR Atmospheres

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The horizontal two-dimensional near-surface structure of a tornadic vortex within a winter storm was analyzed. The tornadic vortex was observed on 10 December 2012 by the high-resolution in situ observational linear array of wind and pressure sensors (LAWPS) system in conjunction with a high-resolution Doppler radar. The 0.1 s maximum wind speed and pressure deficit near the ground were recorded as 35.3 m s À1 and À3.8 hPa, respectively. The horizontal two-dimensional distributions of the tornadic vortex wind and pressure were retrieved by the LAWPS data, which provided unprecedented observational detail on the following important features of the near-surface structure of the tornadic vortex. Asymmetric convergent inflow toward the vortex center existed. Total wind speed was strong to the right and rear side of the translational direction of the vortex and weak in the forward part of the vortex possibly because of the strong convergent inflow in that region. The tangential wind speed profile of the vortex was better approximated using a modified Rankine vortex rather than the Rankine vortex both at 5 m above ground level (agl) and 100 m agl, and other vortex models (Burgers-Rott vortex and Wood-White vortex) were also compared. The cyclostrophic wind balance was violated in the core radius R 0 and outside the core radius in the forward sector; however, it was held with a relatively high accuracy of approximately 14% outside the core of the vortex in the rearward sector (from 2 R 0 to 5 R 0 ) near the ground.

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The Influence of a Local Swirl Ratio on Tornado Intensification near the Surface

Cited by 167 publications

References 15 publications

Studies of the relationship between environmental forcing and the structure and dynamics of tornado-like vortices

Studies of the relationship between environmental forcing and the structure and dynamics of tornado-like vortices

An Overview of Surface Conditions in Numerical Simulations of Dust Devils and the Consequent Near-surface Air Flow Fields

Analysis of the horizontal two‐dimensional near‐surface structure of a winter tornadic vortex using high‐resolution in situ wind and pressure measurements

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