On Modelling Tornadoes in isolation from the Parent Storm

Fiedler, Brian H.

doi:10.1080/07055900.1995.9649542

Cited by 20 publications

(6 citation statements)

References 12 publications

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“…The current inability to do so indicates that least one crucial physical mechanism is still missing [47,53]. The three main approaches that aim to tackle this challenge are observational field campaigns [51,55], simulations of the entire supercell thunderstorm [40], and idealized local laboratory and numerical models of tornado-like vortices (TLVs) [56,57]. (a) Sketch of the cylindrical rotating Rayleigh-Bénard convection system studied here, as well as of the centrifugally driven meridional circulation.…”

Section: Introductionmentioning

confidence: 99%

“…The prototypes of these simplified models are the laboratory Ward chamber and the numerical Fiedler chamber [56,57,59], where, in both cases, the geometry is simplified to a cylinder. In the Ward chamber, the updraft is obtained using mechanical forcing through a fan, and angular momentum is supplied by a rotating screen.…”

Section: Introductionmentioning

confidence: 99%

“…67]. Both the laboratory and the numerical set-ups successfully produce TLVs, and the original as well as the successor models have substantially improved our understanding of tornadoes [56,59,[68][69][70][71][72][73][74][75][76][77].…”

Section: Introductionmentioning

confidence: 99%

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Tornado-like vortices in the quasi-cyclostrophic regime of Coriolis-centrifugal convection

Horn

Aurnou

2021

Journal of Turbulence

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Coriolis-centrifugal convection (C 3 ) in a cylindrical domain constitutes an idealised model of tornadic storms, where the rotating cylinder represents the mesocyclone of a supercell thunderstorm. We present a suite of C 3 direct numerical simulations, analysing the influence of centrifugal buoyancy on the formation of tornado-like vortices (TLVs). TLVs are self-consistently generated provided the flow is within the quasi-cyclostrophic (QC) regime in which the dominant dynamical balance is between pressure gradient and centrifugal buoyancy forces. This requires the Froude number to be greater than the radius-to-height aspect ratio, F r γ. We show that the TLVs that develop in our C 3 simulations share many similar features with realistic tornadoes, such as azimuthal velocity profiles, intensification of the vortex strength, and helicity characteristics. Further, we analyse the influence of the mechanical bottom boundary conditions on the formation of TLVs, finding that a rotating fluid column above a stationary surface does not generate TLVs if centrifugal buoyancy is absent. In contrast, TLVs are generated in the QC regime with any bottom boundary conditions when centrifugal buoyancy is present. Our simulations bring forth insights into natural supercell thunderstorm systems by identifying properties that determine whether a mesocyclone becomes tornadic or remains non-tornadic. For tornadoes to exist, a vertical temperature difference must be present that is capable of driving strong convection. Additionally, our F r γ predictions dimensionally imply a critical mesocyclone angular rotation rate of Ωmc g/Hmc. Taking a typical mesocyclone height of Hmc ≈ 12 km, this translates to Ωmc 3 × 10 −2 s −1 for centrifugal buoyancy-dominated, quasi-cyclostrophic tornadogenesis. The formation of the simulated TLVs happens at all heights on the centrifugal buoyancy time scale τ cb . This implies a roughly 1 minute, height-invariant formation for natural tornadoes, consistent with recent observational estimates.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Tornado-like vortices in the quasi-cyclostrophic regime of Coriolis-centrifugal convection

Horn

Aurnou

2021

Journal of Turbulence

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“…Since this is not possible one often resorts to 'open' boundary conditions, which unfortunately introduce uncertainty (Fiedler 1995).…”

Section: Numerical Experimentsmentioning

confidence: 99%

Secondary circulations in rotating-flow boundary layers

Rotunno¹

2014

AMOJ

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The rotating-flow boundary layer is a special case of the more general threedimensional boundary layer in which the pressure gradient imposed by the outer flow (above the boundary layer) is not in the same direction as the outer flow. The rotating-flow boundary layer thus has motion that is transverse to the streamlines of the outer flow, that is, there is a secondary circulation to the primary circulation of the outer flow. That the secondary circulation can extend far above the boundary layer presents a set of perplexing conceptual problems unlike any encountered in a two-dimensional boundary layer. This paper reviews, critically discusses and presents numerical simulations attempting to supplement existing theory for several canonical problems concerning secondary circulations in rotating-flow boundary layers. Based on the present results, brief comments on atmospheric vortices are made.

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“…Horizontal convergence then amplifies the vertical vorticity as the parcel ascends. Fiedler (1995) compared the solution of a tornado vortex uncoupled from its parent storm in a simple numerical model with a coupled case and found profound differences, while manifesting doubts about the utility of modeling tornadoes isolated from a parent storm. The focus of these simulations was on the tornadogenesis.…”

Section: Different Research Approachesmentioning

confidence: 99%

Large -eddy simulation of a three-dimensional compressible tornado vortex

Xia¹

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Large-Eddy Simulation of a Three-Dimensional Compressible Tornado Vortex Jianjun Xia Large-Eddy simulation (LES) has become a very useful tool for investigating tornadoes, one of the more spectacular and destructive phenomena of nature. A new three-dimensional, unsteady, compressible model is generated to determine how significant the differences between compressible and incompressible LES simulations may be in some extremely violent tornadoes. In particular, this study seeks to determine how high the Mach number within the tornado may become before significant changes occur due to compressibility, and what the major effects of these changes may be expected to be. After developing and verifying the compressible LES model, three different patterns of tornadic corner flows cataloged by local swirl ratio are simulated under quasisteady conditions for different Mach numbers. Simulation comparisons have demonstrated that the compressibility effects are different for different corner flow structures. At peak average Mach numbers less than approximately 0.5, the compressibility effects are not very significant and may be accounted for to leading order by an appropriate isentropic transformation applied to the incompressible results. As the maximum Mach number is increased to more than 1.0, the compressibility effects for low-swirl-ratio corner flows are dramatic, with significant increase in peak vertical velocity and the height of the vortex breakdown above the surface. The effects are much weaker for medium swirl conditions, and expected to be still weaker for high swirl corner flow where the effects are essentially limited to influencing the secondary vortices. In general, compressibility effects would not change the basic dynamics of tornadic corner flows even if Mach numbers greater than one are achieved. c P P ∆ ∆ min versus c S for the incompressible and compressible results at different Mach numbers 5-5-2 Summary of the ratio c V W max versus c S for the incompressible and compressible results at different Mach numbers 5-5-3 Summary of the ratio c t V V max versus c S for the incompressible and compressible results at different Mach numbers 5-5-4 Summary of the ratio max max t

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On Modelling Tornadoes in isolation from the Parent Storm

Cited by 20 publications

References 12 publications

Tornado-like vortices in the quasi-cyclostrophic regime of Coriolis-centrifugal convection

Tornado-like vortices in the quasi-cyclostrophic regime of Coriolis-centrifugal convection

Secondary circulations in rotating-flow boundary layers

Large -eddy simulation of a three-dimensional compressible tornado vortex

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