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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
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
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
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
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
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
); 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
); 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
; 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
; 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
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
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
. 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
. 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
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
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
– 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
– 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
rotational structures, such as bow echo line-end vortices ( Trier et al. 1997 ; Weisman and Davis 1998 ; Meng et al. 2012 ) and mesocyclones ( Rotunno and Klemp 1985 ; Davies-Jones and Brooks 1993 ; Adlerman et al. 1999 ; Markowski et al. 2008 ). However, recent studies have found that surface drag or friction can also be an important source of low-level horizontal vorticity for tornadogenesis. Using a 50-m grid spacing real-data simulation, Schenkman et al. (2014) studied tornadogenesis in the 8
rotational structures, such as bow echo line-end vortices ( Trier et al. 1997 ; Weisman and Davis 1998 ; Meng et al. 2012 ) and mesocyclones ( Rotunno and Klemp 1985 ; Davies-Jones and Brooks 1993 ; Adlerman et al. 1999 ; Markowski et al. 2008 ). However, recent studies have found that surface drag or friction can also be an important source of low-level horizontal vorticity for tornadogenesis. Using a 50-m grid spacing real-data simulation, Schenkman et al. (2014) studied tornadogenesis in the 8
