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1. Introduction Tornadoes have great impact on society, and thus, the mysteries of tornadogenesis have been investigated extensively. Most studies have focused on tornadogenesis in conjunction with the mesocyclones of supercells, which produce the vast majority of significant tornadoes ( Smith et al. 2012 ). The pathway to mesocyclonic tornadogenesis has been conceptualized in three stages ( Davies-Jones et al. 2001 ; Davies-Jones 2015 ): the development of a mesocyclone aloft via
1. Introduction Tornadoes have great impact on society, and thus, the mysteries of tornadogenesis have been investigated extensively. Most studies have focused on tornadogenesis in conjunction with the mesocyclones of supercells, which produce the vast majority of significant tornadoes ( Smith et al. 2012 ). The pathway to mesocyclonic tornadogenesis has been conceptualized in three stages ( Davies-Jones et al. 2001 ; Davies-Jones 2015 ): the development of a mesocyclone aloft via
the environment (also known as barotropic vorticity), or transport of vertical vorticity to the surface. More than one of these processes contributes to the rotation within the low-level mesocyclone ( Klemp and Rotunno 1983 ; Davies-Jones and Brooks 1993 ; A99 ; Markowski et al. 2008 ); however, the relative importance of these processes to tornadogenesis appears to vary among cases. First, modeling studies by Davies-Jones and Brooks (1993) and Grasso and Cotton (1995) found that the
the environment (also known as barotropic vorticity), or transport of vertical vorticity to the surface. More than one of these processes contributes to the rotation within the low-level mesocyclone ( Klemp and Rotunno 1983 ; Davies-Jones and Brooks 1993 ; A99 ; Markowski et al. 2008 ); however, the relative importance of these processes to tornadogenesis appears to vary among cases. First, modeling studies by Davies-Jones and Brooks (1993) and Grasso and Cotton (1995) found that the
diameter of rain and hail distributions (all else being equal) reduced the net surface area of the hydrometeors, thereby reducing evaporative cooling and melting rates. This produced weaker low-level downdrafts and weaker, shallower cold pools. While the precise mechanisms of supercell tornadogenesis are still up for debate, studies have suggested that tornadoes are often linked to the rear flank downdraft (RFD), which can transport vertical vorticity to the surface, baroclinically generate horizontal
diameter of rain and hail distributions (all else being equal) reduced the net surface area of the hydrometeors, thereby reducing evaporative cooling and melting rates. This produced weaker low-level downdrafts and weaker, shallower cold pools. While the precise mechanisms of supercell tornadogenesis are still up for debate, studies have suggested that tornadoes are often linked to the rear flank downdraft (RFD), which can transport vertical vorticity to the surface, baroclinically generate horizontal
is the frictional generation of near-surface horizontal vorticity associated with the intensification of the inflow into the Minco mesovortex. This flow profile takes about 10 min to develop after the genesis of the Minco mesovortex. We speculate that weaker, shorter-lived mesovortices may dissipate before a rotor circulation develops, which could preclude tornadogenesis. The important role of surface drag and the rotor circulation raises a number of questions that will be the focus of future
is the frictional generation of near-surface horizontal vorticity associated with the intensification of the inflow into the Minco mesovortex. This flow profile takes about 10 min to develop after the genesis of the Minco mesovortex. We speculate that weaker, shorter-lived mesovortices may dissipate before a rotor circulation develops, which could preclude tornadogenesis. The important role of surface drag and the rotor circulation raises a number of questions that will be the focus of future
proposed by Davies-Jones (1982) , although speculations about the role of downdrafts in tornadogenesis date back even further (e.g., Ludlam 1963 ). Davies-Jones argued that in an environment with large horizontal vorticity but devoid of vertical vorticity, an updraft alone cannot achieve large vertical vorticity at the surface via vortex-line reorientation. The reason is that as the horizontal vorticity is reoriented into the vertical within the updraft gradient, parcels are rising away from the
proposed by Davies-Jones (1982) , although speculations about the role of downdrafts in tornadogenesis date back even further (e.g., Ludlam 1963 ). Davies-Jones argued that in an environment with large horizontal vorticity but devoid of vertical vorticity, an updraft alone cannot achieve large vertical vorticity at the surface via vortex-line reorientation. The reason is that as the horizontal vorticity is reoriented into the vertical within the updraft gradient, parcels are rising away from the
1. Introduction The rain curtain associated with the hook-shaped appendage to a supercell’s radar echo is usually regarded as a passive indicator of a possible tornado. Close-range airborne and mobile radar observations made during the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX; Rasmussen et al. 1994 ) in 1994–95 and in subsequent follow-up experiments have revealed the presence of a hook echo prior to tornadogenesis in every case. Development of the hook is
1. Introduction The rain curtain associated with the hook-shaped appendage to a supercell’s radar echo is usually regarded as a passive indicator of a possible tornado. Close-range airborne and mobile radar observations made during the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX; Rasmussen et al. 1994 ) in 1994–95 and in subsequent follow-up experiments have revealed the presence of a hook echo prior to tornadogenesis in every case. Development of the hook is
applicable to tornadic phenomena and is made applicable to solve mysteries of tornadogenesis. Furthermore, the balance is a newly found one, because it is different from the other known balance conditions, such as hydrostatic, (quasi-) geostrophic, cyclostrophic, Boussinesq, and anelastic balance. The variational formalism is similar to the one observed by Euler in 1736 and referred to as the Euler equation ( Oden and Reddy 1976 ; Lanczos 1970 ) and later as the Gateaux derivative ( Gateaux 1913 ) in
applicable to tornadic phenomena and is made applicable to solve mysteries of tornadogenesis. Furthermore, the balance is a newly found one, because it is different from the other known balance conditions, such as hydrostatic, (quasi-) geostrophic, cyclostrophic, Boussinesq, and anelastic balance. The variational formalism is similar to the one observed by Euler in 1736 and referred to as the Euler equation ( Oden and Reddy 1976 ; Lanczos 1970 ) and later as the Gateaux derivative ( Gateaux 1913 ) in
1. Introduction Supercells are characterized by a persistent mesocyclone ( Lemon and Doswell 1979 ), and the midlevel [3–6 km above ground level (AGL)] mesocyclone is understood to result mainly from tilting of vorticity associated with the vertical shear of environmental wind ( Davies-Jones 1984 ). While all supercells feature midlevel rotation, some also develop mesocyclones below 2 km AGL, and this development can be important for tornadogenesis. Markowski et al. (1998) investigated the
1. Introduction Supercells are characterized by a persistent mesocyclone ( Lemon and Doswell 1979 ), and the midlevel [3–6 km above ground level (AGL)] mesocyclone is understood to result mainly from tilting of vorticity associated with the vertical shear of environmental wind ( Davies-Jones 1984 ). While all supercells feature midlevel rotation, some also develop mesocyclones below 2 km AGL, and this development can be important for tornadogenesis. Markowski et al. (1998) investigated the
tornadogenesis. For example, Wicker and Wilhelmson (1995) conducted an idealized numerical simulation and showed that a rear-flank downdraft (RFD) plays a role in tornadogenesis. The importance of such downdraft and related baroclinic vorticity generation has been indicated by theoretical ( Davies-Jones and Brooks 1993 ), observational ( Straka et al. 2007 ; Markowski et al. 2008 , 2012a , b ), and recent numerical ( Dahl et al. 2014 ) investigations. The baroclinically generated horizontal vorticity and
tornadogenesis. For example, Wicker and Wilhelmson (1995) conducted an idealized numerical simulation and showed that a rear-flank downdraft (RFD) plays a role in tornadogenesis. The importance of such downdraft and related baroclinic vorticity generation has been indicated by theoretical ( Davies-Jones and Brooks 1993 ), observational ( Straka et al. 2007 ; Markowski et al. 2008 , 2012a , b ), and recent numerical ( Dahl et al. 2014 ) investigations. The baroclinically generated horizontal vorticity and
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
