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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
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 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
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
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
supercell simulations and thus assess the merits of various tornado theories. A subsequent paper will report and lightly test a methodology for computing partial vorticities of a parcel along its forward trajectory. The method requires the parcel’s initial vorticity and, along its path, its velocity-gradient matrix and the torques acting on it. This information can be obtained from the output of a simulation. Although still not providing conclusive evidence in favor of a single tornadogenesis theory
supercell simulations and thus assess the merits of various tornado theories. A subsequent paper will report and lightly test a methodology for computing partial vorticities of a parcel along its forward trajectory. The method requires the parcel’s initial vorticity and, along its path, its velocity-gradient matrix and the torques acting on it. This information can be obtained from the output of a simulation. Although still not providing conclusive evidence in favor of a single tornadogenesis theory
1. Introduction In meteorology, the laws governing mass, energy, momentum, angular momentum, and entropy, should be sacrosanct. In supercell simulations, invented forces should be tolerated only to the extent that they do not fundamentally alter the results. The latest supercell simulations with surface drag have such high resolution that they reproduce strong to violent tornadoes. These simulations seek to understand tornadogenesis. Use of a fictitious force that generates spurious horizontal
1. Introduction In meteorology, the laws governing mass, energy, momentum, angular momentum, and entropy, should be sacrosanct. In supercell simulations, invented forces should be tolerated only to the extent that they do not fundamentally alter the results. The latest supercell simulations with surface drag have such high resolution that they reproduce strong to violent tornadoes. These simulations seek to understand tornadogenesis. Use of a fictitious force that generates spurious horizontal
increased rotation in the mesocyclone led to upward pressure gradient forces that were responsible for generating a strong low-level updraft. In turn, this low-level updraft tilted baroclinically generated horizontal vorticity into the vertical and then stretched it leading to tornadogenesis. WW95 was unable to explain the development of rotation next to the surface and they did not discuss the cause of the midlevel mesocyclone intensification responsible for low-level updraft intensification. Most of
increased rotation in the mesocyclone led to upward pressure gradient forces that were responsible for generating a strong low-level updraft. In turn, this low-level updraft tilted baroclinically generated horizontal vorticity into the vertical and then stretched it leading to tornadogenesis. WW95 was unable to explain the development of rotation next to the surface and they did not discuss the cause of the midlevel mesocyclone intensification responsible for low-level updraft intensification. Most of
low-level shear, LCL, and supercell tornadogenesis are not fully understood, some straightforward hypotheses have been proposed. In terms of shear, stronger low-level shear is often associated with larger storm-relative helicity, implying greater potential for updraft rotation through the tilting and stretching of environmental streamwise vorticity within the supercell updraft, which is responsible for the generation of the midlevel mesocyclone ( Davies-Jones 1984 ). In turn, as rotation aloft
low-level shear, LCL, and supercell tornadogenesis are not fully understood, some straightforward hypotheses have been proposed. In terms of shear, stronger low-level shear is often associated with larger storm-relative helicity, implying greater potential for updraft rotation through the tilting and stretching of environmental streamwise vorticity within the supercell updraft, which is responsible for the generation of the midlevel mesocyclone ( Davies-Jones 1984 ). In turn, as rotation aloft
