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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
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
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
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 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
centered on understanding the processes that govern supercell maturation and subsequent tornadogenesis. The process of supercell mesocyclonic tornadogenesis can be characterized by three steps (e.g., Davies-Jones 2015 ): 1) the formation of a midlevel [e.g., ≈3–7 km above ground level (AGL)] mesocyclone, 2) the generation of vertical vorticity ( ζ ) near the surface, and 3) the formation of a tornado via the contraction (convergence and stretching) of the resultant near-surface ζ . It has long been
centered on understanding the processes that govern supercell maturation and subsequent tornadogenesis. The process of supercell mesocyclonic tornadogenesis can be characterized by three steps (e.g., Davies-Jones 2015 ): 1) the formation of a midlevel [e.g., ≈3–7 km above ground level (AGL)] mesocyclone, 2) the generation of vertical vorticity ( ζ ) near the surface, and 3) the formation of a tornado via the contraction (convergence and stretching) of the resultant near-surface ζ . It has long been
Fluid Dynamics. Cambridge University Press, 615 pp . Benjamin , T. B. , 1968 : Gravity currents and related phenomena . J. Fluid Mech. , 31 , 209 – 248 . Bryan , G. H. , and J. M. Fritsch , 2002 : A benchmark simulation for moist nonhydrostatic numerical models . Mon. Wea. Rev. , 130 , 2917 – 2928 . Davies-Jones , R. P. , 1982a : A new look at the vorticity equation with application to tornadogenesis. Preprints, 12th Conf. on Severe Local Storms, San Antonio, TX, Amer. Meteor
Fluid Dynamics. Cambridge University Press, 615 pp . Benjamin , T. B. , 1968 : Gravity currents and related phenomena . J. Fluid Mech. , 31 , 209 – 248 . Bryan , G. H. , and J. M. Fritsch , 2002 : A benchmark simulation for moist nonhydrostatic numerical models . Mon. Wea. Rev. , 130 , 2917 – 2928 . Davies-Jones , R. P. , 1982a : A new look at the vorticity equation with application to tornadogenesis. Preprints, 12th Conf. on Severe Local Storms, San Antonio, TX, Amer. Meteor
supercell they studied. However, data presented in Finley et al. (2010) and Lee et al. (2012) suggest the thermodynamic properties of internal outflow surges may vary dramatically within a single storm. They analyzed mobile mesonet data from a strongly tornadic supercell and found four internal outflow surges all with different thermodynamic properties during a single low-level mesocyclone occlusion cycle. Warm surges were generally present during times of tornadogenesis and intensification, whereas
supercell they studied. However, data presented in Finley et al. (2010) and Lee et al. (2012) suggest the thermodynamic properties of internal outflow surges may vary dramatically within a single storm. They analyzed mobile mesonet data from a strongly tornadic supercell and found four internal outflow surges all with different thermodynamic properties during a single low-level mesocyclone occlusion cycle. Warm surges were generally present during times of tornadogenesis and intensification, whereas
, while Part III reports on model parameter studies investigating the role of convective available potential energy (CAPE) and ambient vertical and horizontal shear in the evolution of landspouts. Until this past decade most attention in tornado research has been placed on understanding supercell tornadogenesis due to the severity of this type of tornado. NSTs have attracted more recent attention as they affect geographical areas of increasing population density such as the High Plains just east of
, while Part III reports on model parameter studies investigating the role of convective available potential energy (CAPE) and ambient vertical and horizontal shear in the evolution of landspouts. Until this past decade most attention in tornado research has been placed on understanding supercell tornadogenesis due to the severity of this type of tornado. NSTs have attracted more recent attention as they affect geographical areas of increasing population density such as the High Plains just east of
1. Introduction The successful tornadogenesis paradigm must explain why tornadic vortex signatures (TVSs) and embryonic tornadoes are sometimes, but not always, observed aloft prior to tornadogenesis. A TVS is a large value (typically >1 × 10 −2 s −1 ) of azimuthal shear between two adjacent sampling volumes in a Doppler-radar radial-velocity field and usually forms within (but not necessarily in the center of) a mesocyclone (e.g., Brown et al. 1978 ). It is presumed that a TVS is a degraded
1. Introduction The successful tornadogenesis paradigm must explain why tornadic vortex signatures (TVSs) and embryonic tornadoes are sometimes, but not always, observed aloft prior to tornadogenesis. A TVS is a large value (typically >1 × 10 −2 s −1 ) of azimuthal shear between two adjacent sampling volumes in a Doppler-radar radial-velocity field and usually forms within (but not necessarily in the center of) a mesocyclone (e.g., Brown et al. 1978 ). It is presumed that a TVS is a degraded
