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Brett Roberts
,
Ming Xue
,
Alexander D. Schenkman
, and
Daniel T. Dawson II

1. Introduction Despite several decades of intense focus from the research community, our understanding of the physical mechanisms responsible for supercell tornadogenesis remains incomplete. Horizontal vorticity in the prestorm environment has been well established as the primary source for midlevel rotation in supercells ( Davies-Jones 1984 ); by contrast, various potential sources for near-ground vorticity in a tornadic supercell continue to be investigated. A fundamental question underlying

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Paul M. Markowski
and
Yvette P. Richardson

1. Introduction Among the outstanding questions related to tornadogenesis in supercell thunderstorms are the relative roles of environmental horizontal vorticity associated with the ambient vertical wind shear versus the horizontal vorticity that is produced baroclinically by storm-generated horizontal buoyancy gradients, particularly those associated with precipitation regions. Climatological studies derived from proximity soundings repeatedly find that tornadoes are more probable as the

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Jannick Fischer
and
Johannes M. L. Dahl

1. Introduction Supercell tornadogenesis relies on the interaction of two processes: internally produced near-ground vertical vorticity and the strong upward accelerations below the mesocyclone ( Davies-Jones 2015 ). Regarding the first aspect, over the past decades many studies have been performed to find the main source of near-ground vertical vorticity for tornadoes. It has been largely accepted that the initial vertical vorticity arises from the Davies-Jones and Brooks (1993 , hereafter

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Paul M. Markowski
and
Yvette P. Richardson

Markowski 2006 ) and the presence of a strong, upward-directed VPPGF at low levels (an updraft trait associated with strong low-level vertical shear in the environment; MR14 ) are insufficient conditions for tornadogenesis as well, given that not all supercells in environments known to be supportive of these favorable storm attributes produce tornadoes. Fig . 1. Magnitude of the cyclonic vorticity maximum ζ max as a function of the horizontal position of the heat sink relative to the heat source in

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Paul M. Markowski

al. 2014 ; Markowski and Richardson 2014 , hereafter MR14 ). A tornado or tornadolike vortex 1 can develop if this vertical vorticity is subsequently stretched. Tornadogenesis also has been linked to downdrafts in numerous observational studies [see the review by Markowski (2002) ]. Moreover, in the subset of observational studies in which a volume of dual-Doppler observations is available, the configuration of the vortex lines in the tornadic region suggests a strong influence of baroclinity

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Robert Davies-Jones

1. Introduction Vorticity dynamics is fundamental to understanding tornadogenesis (see reviews by Davies-Jones et al. 2001 , hereafter DJ+01 ; Davies-Jones 2015a ). Dutton (1986) showed theoretically that the vorticity of a parcel in inviscid, isentropic flow decomposes into barotropic and baroclinic parts. By using propagators, Epifanio and Durran (2002) and Davies-Jones (2006 , 2015b) extended this work to include vorticity arising from frictional torques, planetary vorticity, and

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Brett Roberts
,
Ming Xue
, and
Daniel T. Dawson II

1. Introduction The role of surface drag in supercell dynamics, and particularly in tornadogenesis, continues to receive heightened research interest during recent years. To a large degree, the present study represents an extension of Roberts et al. (2016 , hereafter R16 ) and Roberts and Xue (2017 , hereafter RX17 ) that examine the effects of surface drag using a fixed drag coefficient C d value of 0.01. As such, we will first summarize those two studies for context, then briefly review

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L. M. Leslie
and
R. K. Smith

JuLY 1978 L. M. L E S L I E A N D R. K. S M I T H 1281The Effect of Vertical Stability on Tornadogenesis L. M. L~.sLmAustralian Nu~nerical Meteorology Research Centre, Melbourne, Australia 3001 R. K. S~r~TI~Department of Mathematics, Monash University, Clayton, Australia 3168(Manuscript received 5 October 1977, in final form 23 January 1978) ABSTRACT A recent numerical

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Robert Davies-Jones

supercell simulations and thus assess the merits of various tornado theories. A subsequent paper will report and lightly test a methodology for computing partial vorticities of a parcel along its forward trajectory. The method requires the parcel’s initial vorticity and, along its path, its velocity-gradient matrix and the torques acting on it. This information can be obtained from the output of a simulation. Although still not providing conclusive evidence in favor of a single tornadogenesis theory

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Robert Davies-Jones

1. Introduction In meteorology, the laws governing mass, energy, momentum, angular momentum, and entropy, should be sacrosanct. In supercell simulations, invented forces should be tolerated only to the extent that they do not fundamentally alter the results. The latest supercell simulations with surface drag have such high resolution that they reproduce strong to violent tornadoes. These simulations seek to understand tornadogenesis. Use of a fictitious force that generates spurious horizontal

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