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JuLY 1978 E D W A R D A. B R A N D E S 995Mesocyclone Evolution and Tornadogenesis: Some Observations EDWARD A. BRANDESNational Severe Storms Laboratory, NOAA, Norman, OK 73069(Manuscript received 15 September 1977, in final form 3 April 1978) ABSTRACT Updraft mesocyclones in tornado-producing thunderstorms form along convergent and cyclonicallysheared boundaries that
JuLY 1978 E D W A R D A. B R A N D E S 995Mesocyclone Evolution and Tornadogenesis: Some Observations EDWARD A. BRANDESNational Severe Storms Laboratory, NOAA, Norman, OK 73069(Manuscript received 15 September 1977, in final form 3 April 1978) ABSTRACT Updraft mesocyclones in tornado-producing thunderstorms form along convergent and cyclonicallysheared boundaries that
tornadogenesis following the interaction between a supercell and other convection have been documented by Wolf (1998) , Sabones et al. (1996) , Goodman and Knupp (1993) , and Bullas and Wallace (1988) . The connection between cell merger and tornadogenesis in this case will be discussed further in Part II. As quickly as the convection intensified near the updraft merger point, it weakened, and by 0021 UTC updrafts in the region were 14–18 m s −1 at z = 6.1 km. All during this time period, S1 (which
tornadogenesis following the interaction between a supercell and other convection have been documented by Wolf (1998) , Sabones et al. (1996) , Goodman and Knupp (1993) , and Bullas and Wallace (1988) . The connection between cell merger and tornadogenesis in this case will be discussed further in Part II. As quickly as the convection intensified near the updraft merger point, it weakened, and by 0021 UTC updrafts in the region were 14–18 m s −1 at z = 6.1 km. All during this time period, S1 (which
addresses nonsupercell tornadogenesis. Closest to it is a suggestion for dust devil formation by Barcilon and Drazin (1972) in terms of Kelvin–Helmholtz and Rayleigh–Taylor instability, but a dust devil is distinctly much smaller, shallower, and weaker than a NST. While an intense localized surface heating must be a crucial factor for dust devil, it is not the case for NST. There is a numerical simulation study of NST with some success ( Lee and Wilhelmson 1997 , LW97 hereafter). They used a high
addresses nonsupercell tornadogenesis. Closest to it is a suggestion for dust devil formation by Barcilon and Drazin (1972) in terms of Kelvin–Helmholtz and Rayleigh–Taylor instability, but a dust devil is distinctly much smaller, shallower, and weaker than a NST. While an intense localized surface heating must be a crucial factor for dust devil, it is not the case for NST. There is a numerical simulation study of NST with some success ( Lee and Wilhelmson 1997 , LW97 hereafter). They used a high
1. Introduction In Part I of this series of articles on the simulation of nonsupercell tornadogenesis (NSTG), misocyclone initiation and evolution were investigated along outflow boundaries possessing significant across-front horizontal shear with a dry, nonhydrostatic, three-dimensional numerical model ( Lee and Wilhelmson 1997, hereafter LW97) . Misocyclone circulations, which by definition ( Fujita 1981 ) have diameters less than 4 km, are the parent circulations of nonsupercell tornadoes
1. Introduction In Part I of this series of articles on the simulation of nonsupercell tornadogenesis (NSTG), misocyclone initiation and evolution were investigated along outflow boundaries possessing significant across-front horizontal shear with a dry, nonhydrostatic, three-dimensional numerical model ( Lee and Wilhelmson 1997, hereafter LW97) . Misocyclone circulations, which by definition ( Fujita 1981 ) have diameters less than 4 km, are the parent circulations of nonsupercell tornadoes
the positive ω 0 × N ⋅ d x . c. Vortex formation in axisymmetric flow In axisymmetric simulations of tornadogenesis (e.g., Markowski et al. 2003 ; Davies-Jones 2008 ), L ( t ) would be a horizontal circle of variable radius σ ( t ) centered on the axis. In this section, M represents angular momentum. The circulation Γ is related to M by Γ ≡ 2 πM . In cylindrical coordinates ( r , ϕ , z ) with corresponding wind components ( u r , M / r , w ), imposing axisymmetry on (7) yields
the positive ω 0 × N ⋅ d x . c. Vortex formation in axisymmetric flow In axisymmetric simulations of tornadogenesis (e.g., Markowski et al. 2003 ; Davies-Jones 2008 ), L ( t ) would be a horizontal circle of variable radius σ ( t ) centered on the axis. In this section, M represents angular momentum. The circulation Γ is related to M by Γ ≡ 2 πM . In cylindrical coordinates ( r , ϕ , z ) with corresponding wind components ( u r , M / r , w ), imposing axisymmetry on (7) yields
. 1997 ; Bluestein and Pazmany 2000 ; Bluestein and Wakimoto 2003 ), a considerable number of high-resolution kinematic datasets have been obtained from tornadic supercells. Given the difficulty involved in positioning near-surface observing systems, far fewer datasets, either mobile mesonet ( Straka et al. 1996 ) or StickNet ( Weiss and Schroeder 2008 ), exist to describe proximate tornado or tornadogenesis region thermodynamic and kinematic characteristics. Only a few mesonet studies provide a
. 1997 ; Bluestein and Pazmany 2000 ; Bluestein and Wakimoto 2003 ), a considerable number of high-resolution kinematic datasets have been obtained from tornadic supercells. Given the difficulty involved in positioning near-surface observing systems, far fewer datasets, either mobile mesonet ( Straka et al. 1996 ) or StickNet ( Weiss and Schroeder 2008 ), exist to describe proximate tornado or tornadogenesis region thermodynamic and kinematic characteristics. Only a few mesonet studies provide a
1. Introduction Most attention in tornado research has been placed on understanding supercell tornadogenesis due to the severity of this type of tornado; however, in the past decade, nonsupercell tornadoes (NSTs) have attracted increasing attention as they affect geographical areas of expanding population such as the High Plains just east of the Front Range and the Florida peninsula. For instance, near and just east of the Denver to Ft. Collins corridor, NSTs account for a large majority of the
1. Introduction Most attention in tornado research has been placed on understanding supercell tornadogenesis due to the severity of this type of tornado; however, in the past decade, nonsupercell tornadoes (NSTs) have attracted increasing attention as they affect geographical areas of expanding population such as the High Plains just east of the Front Range and the Florida peninsula. For instance, near and just east of the Denver to Ft. Collins corridor, NSTs account for a large majority of the
1. Introduction Despite a growing body of literature describing observations of tornadogenesis and dissipation ( Roberts and Wilson 1995 ; Wakimoto and Atkins 1996 ; Dowell and Bluestein 1997 , 2002b ; Wakimoto and Liu 1998 ; Dunn and Vasiloff 2001 ; Ziegler et al. 2001 ; Bluestein and Wakimoto 2003 ; Bluestein et al. 2003 ; Wakimoto et al. 2004 ; Van Den Broeke et al. 2008 ; Wurman et al. 2007 , 2010 ; Markowski and Richardson 2009 ; Palmer et al. 2011 ; Marquis et al. 2012
1. Introduction Despite a growing body of literature describing observations of tornadogenesis and dissipation ( Roberts and Wilson 1995 ; Wakimoto and Atkins 1996 ; Dowell and Bluestein 1997 , 2002b ; Wakimoto and Liu 1998 ; Dunn and Vasiloff 2001 ; Ziegler et al. 2001 ; Bluestein and Wakimoto 2003 ; Bluestein et al. 2003 ; Wakimoto et al. 2004 ; Van Den Broeke et al. 2008 ; Wurman et al. 2007 , 2010 ; Markowski and Richardson 2009 ; Palmer et al. 2011 ; Marquis et al. 2012
initiated by intense wildfires: Numerical simulations of pyro-convection and pyro-tornadogenesis . Geophys. Res. Lett. , 36 , L12812 , https://doi.org/10.1029/2009GL039262 . Cunningham , P. , S. L. Goodrick , M. Y. Hussaini , and R. R. Linn , 2005 : Coherent vortical structures in numerical simulations of buoyant plumes from wildland fires . Int. J. Wildland Fire , 14 , 61 – 75 , https://doi.org/10.1071/WF04044 . Dowdy , A. J. , H. Ye
initiated by intense wildfires: Numerical simulations of pyro-convection and pyro-tornadogenesis . Geophys. Res. Lett. , 36 , L12812 , https://doi.org/10.1029/2009GL039262 . Cunningham , P. , S. L. Goodrick , M. Y. Hussaini , and R. R. Linn , 2005 : Coherent vortical structures in numerical simulations of buoyant plumes from wildland fires . Int. J. Wildland Fire , 14 , 61 – 75 , https://doi.org/10.1071/WF04044 . Dowdy , A. J. , H. Ye
other wind-shift lines within the storm and occasionally migrate toward the low-level mesocyclone center, subsequently being absorbed into the broader circulation ( Dowell et al. 2002 ; Finley et al. 2002 ; Bluestein et al. 2003 ; Lee et al. 2012 ; Richardson et al. 2012 ; Snyder et al. 2013 ). It is unclear whether the vortices play a role in tornadogenesis or tornado maintenance, which are topics beyond the scope of this paper. Given their regular spacing, it seems likely that these vortices
other wind-shift lines within the storm and occasionally migrate toward the low-level mesocyclone center, subsequently being absorbed into the broader circulation ( Dowell et al. 2002 ; Finley et al. 2002 ; Bluestein et al. 2003 ; Lee et al. 2012 ; Richardson et al. 2012 ; Snyder et al. 2013 ). It is unclear whether the vortices play a role in tornadogenesis or tornado maintenance, which are topics beyond the scope of this paper. Given their regular spacing, it seems likely that these vortices
