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Richard E. Carbone

determined to be temporally coincident withthe tornadic phase. Interpretation of tornadogenesis in supercells is made in the perspective of these observations and thefindings associated with fine-scale numerical simulations. A concluding hypothesis is that the major featuresof tornadogenesis are not particularly sensitive to many aspects of storm-scale circulations but rather theyrequire creation of specific localized conditions along the storm outflow boundary. One such condition is theexistence of a

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Louis J. Wicker
and
Robert B. Wilhelmson

, in final form 3 March 1995)ABSTRACT A three-dimensional numerical simulation using a two-way interactive nested grid is used to study tornadogenesis within a supercell. During a 40-minute period, two tornadoes grow and decay within the storm's mesocyclone. The tornadoes have life spans of approximately 10 minutes. Maximum ground-relative surface windspeeds exceed 60 m s-~ during both tornadoes, and horizontal pressure gradients reach 18 hPa km-~ during thesecond tornado. Comparison of the

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R. Jeffrey Trapp
and
Brian H. Fiedler

sequence of events that leads to tornadogenesis. The "pseudostorm" is an idealized thunderstorm representation and emulates the storm-relative flow, into an updraft, of the horizontal streamwise vorticity that is baroclinically generated in cold air outflow. By not explicitly simulating the morphology of a tornadic thunderstorm, but instead concentrating on the development of low-level rotationand tornado-scale vortices, the authors are able to transcend many of the experimental limitations encountered

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Adam L. Houston

to the explanation for the associative relationship between low-level vertical shear and the occurrence of significant tornadoes. Tornadogenesis, the formation of a concentrated vortex in contact with the cloud and the ground, requires amplification of surface vertical vorticity to tornado strength through convergence–stretching often associated with the storm’s airmass boundaries or self-generated as in the dynamic pipe effect ( Trapp and Davies-Jones 1997 ). Therefore, it can be deduced that

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D. C. Lewellen
and
W. S. Lewellen

idealized steps progressing from large scales to small: the origin of rotation at midlevels within the storm, low-level mesocyclogenesis, tornadogenesis, and tornado structure [see, e.g., Davies-Jones et al. (2001) for a recent review]. The subject of the present work—the near-surface intensification of a vortex due to fluid-dynamic effects—is potentially important in the last three of these. In the basic mechanism the combination of reduced swirl velocity near the surface and a strong radial pressure

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Daniel T. Dawson II
,
Ming Xue
,
Alan Shapiro
,
Jason A. Milbrandt
, and
Alexander D. Schenkman

1. Introduction The possibility that the thermodynamic characteristics of tornado inflow air may have a substantial impact on supercell tornadogenesis and tornado maintenance has been recognized for some time ( Ludlam 1963 ). Leslie and Smith (1978) performed axially symmetric idealized simulations of vortices stretched by an imposed updraft aloft and imposed swirl velocity on the cylindrical boundary and investigated the effect of increasing low-level static stability on the development of

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John M. Peters
,
Christopher J. Nowotarski
,
Jake P. Mulholland
, and
Richard L. Thompson

over subsequent decades reaffirmed the connection between supercell updraft rotational attributes and the tilting of initially horizontal ω s into the vertical direction (e.g., Rotunno and Klemp 1982 , 1985 ; Klemp 1987 ; Weisman and Rotunno 2000 ; Davies-Jones 2002 ). More recent research has also shown that SRH in the lowest 500 m of the atmosphere plays a key role in tornadogenesis (e.g., Parker 2014 ; Coffer et al. 2017 ; Coffer and Parker 2017 , 2018 ; Coffer et al. 2019

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Jason Naylor
and
Matthew S. Gilmore

tornadogenesis or tornadogenesis failure. Acknowledgments The authors thank Dr. Paul Markowski for bringing this error to their attention. REFERENCE Naylor , J. , and M. S. Gilmore , 2014 : Vorticity evolution leading to tornadogenesis and tornadogenesis failure in simulated supercells . J. Atmos. Sci. , 71 , 1201 – 1217 , doi: 10.1175/JAS-D-13-0219.1 .

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Brice E. Coffer
and
Paul M. Markowski

) ]. Table 1. Details of CM1 configuration from C17a and C17b . In section 3 , relationships between updraft, downdraft, and near-ground and midlevel mesocyclone areas are compared using two different evaluation times. The first method uses the key time period of tornadogenesis or tornadogenesis failure as described in C17b , while the second method uses the same definitions and approach as T17 . In either case, following T17 , we define core areas of updraft, downdraft, and mesocyclones by using

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R. K. Smith
,
J. V. Mansbridge
, and
L. M. Leslie

ustralian Numerical Meteorology Research Centre, Melbourne, A ustralia 3000 -. 24 August 1976 We are interested in the recent suggestion byEskridge and Das (1976) that tornadogenesis might beinitiated by the re-ascent of a pool of buoyant air, previously forced to low levels by an intense rain- or haildriven dcwndraft in an otherwise stably stratified subcloud layer. However, ~ertain aspects of the numericalmodel which they use to demonstrate their

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