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Zhanxiang Hua
and
Daniel R. Chavas

heterogeneity affects tornadoes via a variety of research techniques. Historical case study analysis has demonstrated that tornadoes may form along preferred terrain orientations such as ridges and valleys ( Gallimore and Lettau 1970 ), including within large mountain ranges ( Prociv 2012 ). Topography may enhance tornadogenesis both directly via vortex stretching in downslope flow and indirectly by promoting development of the parent convective cell via enhanced mesoscale low-level wind shear caused by

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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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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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Paul Markowski
,
Yvette Richardson
,
James Marquis
,
Joshua Wurman
,
Karen Kosiba
,
Paul Robinson
,
David Dowell
,
Erik Rasmussen
, and
Robert Davies-Jones

. 3. Unedited logarithmic radar reflectivity factor (dB Z ) observed by the KCYS WSR-88D (0.5° elevation angle) and DOW7 radars (1° elevation angle) at (a) 2107:04, (b) 2116:14, (c) 2125:23, (d) 2132:26, (e) 2140:06, and (f) 2148:07 UTC (“ t − X min” indicates X min prior to tornadogenesis). The DOW7 reflectivity is uncalibrated. Fig . 4. Large-scale depiction of the track of the Goshen County storm on 5 Jun 2009 as evidenced by the 40-, 50-, and 60-dB Z isopleths of logarithmic reflectivity

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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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Paul Markowski
,
Yvette Richardson
,
James Marquis
,
Robert Davies-Jones
,
Joshua Wurman
,
Karen Kosiba
,
Paul Robinson
,
Erik Rasmussen
, and
David Dowell

1. Introduction One focus of our ongoing research is the relative role of environmental vorticity versus storm-generated vorticity in tornadogenesis and maintenance. In supercell environments, which are characterized by relatively large vertical shear of the horizontal wind, the horizontal vorticity is typically on the order of 10 −2 s −1 in the lower troposphere. In contrast, vorticity can be generated internally within a storm by horizontal buoyancy gradients (i.e., baroclinity). The

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