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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
LMCs ( Markowski et al. 2002 , 2003 , 2008 ; Straka et al. 2007 ). Because this horizontal vorticity and convective updraft are intensified by environmental low-level vertical shear and water vapor, respectively, the preexisting low-level environment is especially important for tornadogenesis ( Thompson et al. 2003 ; Craven and Brooks 2004 ; Markowski and Richardson 2014 ; Parker and Dahl 2015 ). Even in the presence of MMCs and LMCs, however, tornadoes are not necessarily generated. Trapp
LMCs ( Markowski et al. 2002 , 2003 , 2008 ; Straka et al. 2007 ). Because this horizontal vorticity and convective updraft are intensified by environmental low-level vertical shear and water vapor, respectively, the preexisting low-level environment is especially important for tornadogenesis ( Thompson et al. 2003 ; Craven and Brooks 2004 ; Markowski and Richardson 2014 ; Parker and Dahl 2015 ). Even in the presence of MMCs and LMCs, however, tornadoes are not necessarily generated. Trapp
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
1. Introduction To understand the mechanism of supercell tornadogenesis, identifying the responsible vorticity sources is a vitally important issue. Despite several decades of study on this issue, a complete understanding remains ambiguous. Previous studies included field observations and idealized numerical simulations. It was suggested that the baroclinic effects are prominent in generating the vorticity of tornadoes (e.g., Davies-Jones and Brooks 1993 ; Adlerman et al. 1999 ; Straka et al
1. Introduction To understand the mechanism of supercell tornadogenesis, identifying the responsible vorticity sources is a vitally important issue. Despite several decades of study on this issue, a complete understanding remains ambiguous. Previous studies included field observations and idealized numerical simulations. It was suggested that the baroclinic effects are prominent in generating the vorticity of tornadoes (e.g., Davies-Jones and Brooks 1993 ; Adlerman et al. 1999 ; Straka et al
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
radar near the damage paths of the corresponding tornadoes ( Fig. 1a ). Since the radar was not in full operational mode, and had performed only three scans at the lower elevation angles around the time of the tornadogenesis, they were unable to clarify the detailed relationship between the mesovortices and tornadogenesis. A maximum surface wind of 35 m s −1 ( Fig. 1b ) with rapid change in wind direction from east to west was observed by an anemometer located at the southern end of the runway at
radar near the damage paths of the corresponding tornadoes ( Fig. 1a ). Since the radar was not in full operational mode, and had performed only three scans at the lower elevation angles around the time of the tornadogenesis, they were unable to clarify the detailed relationship between the mesovortices and tornadogenesis. A maximum surface wind of 35 m s −1 ( Fig. 1b ) with rapid change in wind direction from east to west was observed by an anemometer located at the southern end of the runway at
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
heterogeneity affects tornadoes via a variety of research techniques. Historical case study analysis has demonstrated that tornadoes may form along preferred terrain orientations such as ridges and valleys ( Gallimore and Lettau 1970 ), including within large mountain ranges ( Prociv 2012 ). Topography may enhance tornadogenesis both directly via vortex stretching in downslope flow and indirectly by promoting development of the parent convective cell via enhanced mesoscale low-level wind shear caused by
heterogeneity affects tornadoes via a variety of research techniques. Historical case study analysis has demonstrated that tornadoes may form along preferred terrain orientations such as ridges and valleys ( Gallimore and Lettau 1970 ), including within large mountain ranges ( Prociv 2012 ). Topography may enhance tornadogenesis both directly via vortex stretching in downslope flow and indirectly by promoting development of the parent convective cell via enhanced mesoscale low-level wind shear caused by
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
