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Robert Davies-Jones

1. Introduction The question of whether certain air parcels near the ground can rise significantly is crucial to convective initiation and the dynamics of severe convective storms and tornadoes. For example, tornadogenesis may seem imminent based on radar observations but will not occur if surface-based parcels (below the radar horizon) are too negatively buoyant for a vortex aloft to draw them inward and upward ( Leslie and Smith 1978 ; Markowski et al. 2002 , 2003 ). Buoyancy normally is

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Lans P. Rothfusz

generated,tilted vertically and finally enhanced by stretching isrequired. The objective of this experiment, then, is tosee if a tornado-like vortex can be created whose primary net vorticity supply is vertical shear of the horizontal wind. Although the importance of boundarylayer vorticity in tornadogenesis processes has beensuggested (Rotunno, 1980), its contribution to mesocyclone-like flow in the TVC will be considered negligible.2. Simulator characteristics Recently, the vortex chamber at the

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Brian J. Gaudet
and
William R. Cotton

); the cause has been confirmed by observations ( Barnes 1970 ), analysis ( Rotunno 1981 ; Davies-Jones 1984 ), and numerical modeling ( Schlesinger 1975 ; Klemp and Wilhelmson 1978a , b ; Wilhelmson and Klemp 1981 ; Weisman and Klemp 1982 ) to be the interaction of environmental horizontal vorticity and convection-produced updrafts. Lemon and Doswell (1979) observed, however, that prior to tornadogenesis, the vertical vorticity maximum tends to migrate to the updraft–downdraft interface, and

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Matthew Brown
and
Christopher J. Nowotarski

; Craven and Brooks 2004 ). However, the existence of a supercell does not guarantee tornadogenesis—rather, only a fraction of supercells produce tornadoes ( Trapp et al. 2005 ). Thus, identifying factors that differentiate nontornadic and tornadic supercells is crucial, both for our physical understanding of these storms and for forecasting and warning of tornadoes. Two parameters in the near-storm environment have shown skill in distinguishing between nontornadic and tornadic supercells: low-level (0

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Robert J. Trapp
,
Geoffrey R. Marion
, and
Stephen W. Nesbitt

“sometimes as much as 25 min apart.” CM18 (p. 4049) also noted that when they analyzed values “at the time of tornadogenesis/tornadogenesis failure,” minimal to no correlations were found. In fact, per the physical reasoning presented by TMN17 , we would not have expected high correlations between contemporaneously analyzed values (which, incidentally, is why we did not pursue the type of analysis that CM18 conducted in their Fig. 1). To illustrate the expected time lag between, for example, peak

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Lewis D. Grasso
and
William R. Cotton

in this study is the only one responsible for tornado formation. Wicker and Wilhelmson (1993) also did a simulation of tornadogenesis with a different model. Unlikeours, they spawned a fine grid some 20 min before thetornado formed. The process of tornadogenesis in theirrun appears to be very similar to ours. Regardless ofthe actual mechanism responsible for the excitation ofthe elevated vortex, the minimum of the pressure fieldlocated in the horizontal gradient of the updraft, thesubsequent

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Paul M. Markowski
and
Jerry Y. Harrington

storms occurring earlier in the day) may have similarly important dynamical consequences. For instance, when a storm crosses the outflow boundary left behind by some other region of convection, the storm may ingest enhanced baroclinic horizontal vorticity residing along the outflow boundary, which may lead to rapid intensification of low-level rotation (and often tornadogenesis), following tilting and stretching of the augmented horizontal vorticity ( Purdom 1976 ; Maddox et al. 1980 ; Weaver and

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Geoffrey R. Marion
and
Robert J. Trapp

. 2012 ). Though the details of the internal processes associated with QLCS tornadogenesis and tornado intensification likely differ from those of supercell tornadogenesis and intensification, the similar environments supportive of strong QLCS and supercell tornadoes ( Thompson et al. 2012 ) suggest some commonalities in basic processes and, consequently, suggests possible applicability of numerous studies of supercell tornadogenesis to the topic of QLCS tornado intensity explored herein. For example

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John M. Peters
,
Brice E. Coffer
,
Matthew D. Parker
,
Christopher J. Nowotarski
,
Jake P. Mulholland
,
Cameron J. Nixon
, and
John T. Allen

1. Introduction Essential to the understanding and prediction of supercell tornadoes is a fundamental understanding of the processes that regulate their parent low-level mesocyclone. 1 This is because the pressure perturbations within supercell mesocyclones result in strong near-surface vertical accelerations (e.g., Rotunno and Klemp 1985 ), which vertically stretch near-ground vertical vorticity contributing to tornadogenesis (e.g., Doswell and Burgess 1993 ; Wicker and Wilhelmson

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Matthew D. Flournoy
and
Erik N. Rasmussen

– 2194 , https://doi.org/10.1175/JAS3965.1 . Markowski , P. M. , 2016 : An idealized numerical simulation investigation of the effects of surface drag on the development of near-surface vertical vorticity in supercell thunderstorms . J. Atmos. Sci. , 73 , 4349 – 4385 , https://doi.org/10.1175/JAS-D-16-0150.1 . Markowski , P. M. , and Y. P. Richardson , 2014 : The influence of environmental low-level shear and cold pools on tornadogenesis: Insights from idealized simulations . J. Atmos

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