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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
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
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
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
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
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
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
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
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
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
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
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
1. Introduction Vortex breakdown, a rather well-known phenomenon in fluid mechanics, has been documented in tornadoes ( Pauley and Snow 1988 ; see also Lugt 1989 ). The existence of vortex breakdown in tornadic mesocyclones has been inferred from observations of a downdraft near the central axis of the mesocyclonic vortex ( Brandes 1978 ; Wakimoto and Liu 1998 ); tornadogenesis was attributed by these authors to the purported mesocyclonic vortex breakdown. Numerical models, however, have
1. Introduction Vortex breakdown, a rather well-known phenomenon in fluid mechanics, has been documented in tornadoes ( Pauley and Snow 1988 ; see also Lugt 1989 ). The existence of vortex breakdown in tornadic mesocyclones has been inferred from observations of a downdraft near the central axis of the mesocyclonic vortex ( Brandes 1978 ; Wakimoto and Liu 1998 ); tornadogenesis was attributed by these authors to the purported mesocyclonic vortex breakdown. Numerical models, however, have
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
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
1979 ; Doswell 1985 ). It has been suggested that the temperature field in and near a low-level mesocyclone, particularly that associated with the rear-flank downdraft (RFD), may play a role in tornadogenesis ( Davies-Jones et al. 2001 ; Markowski et al. 2002 ). Previous field studies tested this hypothesis using mobile in situ instruments to measure thermodynamic variables in and around the tornado’s parent mesocyclone. While the collection of mobile in situ data was often successful, the
1979 ; Doswell 1985 ). It has been suggested that the temperature field in and near a low-level mesocyclone, particularly that associated with the rear-flank downdraft (RFD), may play a role in tornadogenesis ( Davies-Jones et al. 2001 ; Markowski et al. 2002 ). Previous field studies tested this hypothesis using mobile in situ instruments to measure thermodynamic variables in and around the tornado’s parent mesocyclone. While the collection of mobile in situ data was often successful, the
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
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
