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Edward A. Brandes
,
Robert P. Davies-Jones
, and
Brenda C. Johnson

. REFERENCESAndrt, J. C., and M. Lesieur, 1977: Influence of helicity on the evo lution of isotropic turbulence at high Reynolds number. J. Fluid Mech., 81, 187-207.Barnes, S. L., 1978: Oklahoma thunderstorms on 29-30 April 1970. Part I: Morphology ofa tornadic storm. Mon. Wea. Rev., 106, 673-684.Brandes, E. A., 1978: Mesocyclone evolution and tornadogenesis: Some observations. Mort. Wea. Rev., 106, 995-1011.--, 1981: Finestructure of the Del City-Edmond tornadic mesocirculation. Mon. Wea. Rev., !09

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Rachel L. Storer
,
Susan C. van den Heever
, and
Graeme L. Stephens

. Pollution can lead to important changes in the cold pools produced by storms (e.g., van den Heever and Cotton 2007 ) and appear to even have a role in determining storm organization and the possibility of tornadogenesis (e.g., Lerach et al. 2008 ; Snook and Xue 2008 ). Both modeling and observational studies have been used to examine the effects of increased CCN concentrations in warm clouds. Each method has its own advantages and disadvantages. For example, idealized modeling studies can be used to

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Lans P. Rothfusz
and
Douglas K. Lilly

VOL. 46, No. 14 FIG. 1 la. Trajectories of parcels arriving at radius of 30 cm and aheight of 40 cm. The + indicates the ending point. Each dot indicatesa crossing of height levels which are multiples of five (i.e., z = 5, 10,etc.). Closely bunched dots therefore indicate rapid upward movement.of the significance of this experiment to the tornadogenesis problem. We first consider the case when the vanes are parallelat all levels, so that, Upon neglecting boundary effects,potential flow is

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Karen Kosiba
and
Joshua Wurman

, Kansas, tornado. Preprints, 21st Conf. on Severe Local Storms, San Antonio, TX, Amer. Meteor. Soc., 12.3. [Available online at http://ams.confex.com/ams/pdfpapers/47335.pdf ] . Dowell , D. C. , C. R. Alexander , J. M. Wurman , and L. J. Wicker , 2005 : Centrifuging of hydrometeors and debris in tornadoes: Radar-reflectivity patterns and wind-measurement errors. Mon. Wea. Rev. , 133 , 1501 – 1524 . Fiedler , B. H. , 1993 : Numerical simulations of axisymmetric tornadogenesis in

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Junshi Ito
,
Hiroshi Niino
, and
Mikio Nakanishi

tornadogenesis. While they calculated the circulation using a line integral, we calculated the circulation using an area integral of vorticity over a material surface (MS), which has an advantage of giving additional information about how tilting and stretching of vorticity take place. The next section describes a numerical simulation of DDVs in a convective mixed layer, performed at a very fine resolution. Section 3 describes results of the backward-trajectory analysis on the circulation. The results are

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Charles A. Doswell III

Forecasting and Anal ysis, Seattle, Amer. Meteor. Soc., 300-303.Kessler, E., 1969: On the Distribution and Continuity of Water Sub stance in Atmospheric Circulations. Meteor. Monogr., No. 32, Amer. Meteor. Soc., 84 pp.Lemon, L. R. and C. A. Doswell III, 1979: Severe thunderstorm evolution and mesocyclone structure as related to tornadogenesis. Mon. Wea. Rev., 107, 1189-1197.Miller, J. E., 1948: On the concept of frontogenesis. J. Meteor., 5, 169-171.Petterssen, S., 1956: Weather Analysis and

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P.S. Ray
,
B.C. Johnson
,
K.W. Johnson
,
J.S. Bradberry
,
J.J. Stephens
,
K.K Wagner
,
R.B. Wilhelmson
, and
J.B. Klemp

by the entire radar network, the updraft, reflectivity, and vorticity evolution through the tornadic phase nearly paralleledthat of the Del City storm.' Further understahding of these storms and theirinteraction is developed in other studies. In one related study, Brandes (1981) discusses tornadogenesis around the time of tornado occurrence for one ofthe storms investigated here (Del City). Johnsonet al. (1980)7 present a preliminary overview of thestorm discussed in this paper. Johnson et al

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D. C. Lewellen
,
W. S. Lewellen
, and
J. Xia

vortex meets the ground, this region is of particular relevance, typically being the scene of the largest velocities, lowest pressures, sharpest velocity gradients, and greatest damage potential in the entire flow. In concentrating on this part of the flow we knowingly set aside the important question of tornadogenesis on the larger scale, that is, of how the storm-scale flow gives rise to and maintains the swirling, converging plume on the few kilometer scale that makes the occurrence of an intense

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Erik R. Nielsen
and
Russ S. Schumacher

mechanism by which rotation could potentially enhance rain rates. Although the influence of the VPPGF has been investigated in regards to supercells and tornadogenesis, little attention has been devoted to its impact on precipitation processes when supercells or embedded mesovortices are present. On the convective scale, cells that produce the most extreme rain rates have been shown to be associated with a positive potential vorticity (PV) monopole, compared to the expected PV dipole that is seen in

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John M. Peters
,
Christopher J. Nowotarski
, and
Hugh Morrison

velocities in supercells facilitate production of the largest observed hailstones on Earth (e.g., Wakimoto et al. 2004 ), produce higher cross-tropopause mass transport than ordinary convection ( Mullendore et al. 2005 ) and result in a higher mass detrainment level ( Mullendore et al. 2013 ). Furthermore, supercell updrafts are capable of producing intense low-level vertical accelerations and associated stretching of vertical vorticity, which facilitates tornadogenesis ( Markowski and Richardson 2014

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