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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
1. Introduction Despite major advances in our understanding of supercell tornadoes over the past two decades, skillful, short-term (0–1 h) forecasting (i.e., “nowcasting”) of tornadogenesis remains elusive owing to a lack of understanding of the complicated processes involved and a dearth of observations at the spatiotemporal scales commensurate with the process. Work to distinguish differences between tornadic and nontornadic supercells are ongoing using both observations and numerical
1. Introduction Despite major advances in our understanding of supercell tornadoes over the past two decades, skillful, short-term (0–1 h) forecasting (i.e., “nowcasting”) of tornadogenesis remains elusive owing to a lack of understanding of the complicated processes involved and a dearth of observations at the spatiotemporal scales commensurate with the process. Work to distinguish differences between tornadic and nontornadic supercells are ongoing using both observations and numerical
reflectivity isopleth observed by DOW7 also is overlaid at 0108, 0116, 0124, and 0132 UTC (blue contours). The locations of the photographs that appear in Figs. 11a–c are indicated by the green, black, and purple camera icons, respectively (the photograph time are indicated beside the icons). Following a brief explanation of the available data and the analysis methods in section 2 , a detailed description of the chain of events that led to tornadogenesis are presented in sections 3 and 4 . The
reflectivity isopleth observed by DOW7 also is overlaid at 0108, 0116, 0124, and 0132 UTC (blue contours). The locations of the photographs that appear in Figs. 11a–c are indicated by the green, black, and purple camera icons, respectively (the photograph time are indicated beside the icons). Following a brief explanation of the available data and the analysis methods in section 2 , a detailed description of the chain of events that led to tornadogenesis are presented in sections 3 and 4 . The
1. Introduction Tornadic storms, and tornadogenesis in supercellular storms have been observed visually, with surface observations, and with radars for decades (e.g., Stout and Huff 1953 ; Ludlam 1963 ; Fujita 1975 ; Ray et al. 1975 , 1981 ; Brandes 1977 , 1978 , 1981 , 1984a ; Fujita and Wakimoto 1982 ; Brandes et al. 1988 ; Dowell and Bluestein 1997 , 2002a , b ; Wakimoto and Liu 1998 ; Trapp 1999 ; Trapp et al. 1999 ; Wakimoto and Cai 2000 ; Bluestein
1. Introduction Tornadic storms, and tornadogenesis in supercellular storms have been observed visually, with surface observations, and with radars for decades (e.g., Stout and Huff 1953 ; Ludlam 1963 ; Fujita 1975 ; Ray et al. 1975 , 1981 ; Brandes 1977 , 1978 , 1981 , 1984a ; Fujita and Wakimoto 1982 ; Brandes et al. 1988 ; Dowell and Bluestein 1997 , 2002a , b ; Wakimoto and Liu 1998 ; Trapp 1999 ; Trapp et al. 1999 ; Wakimoto and Cai 2000 ; Bluestein
1. Introduction Significant progress has been made in our understanding of supercell storms through Doppler radar measurements and three-dimensional numerical simulations. However, our knowledge of the dynamics of tornadogenesis in supercell storms is still limited because of difficulties in collecting detailed observational data with good spatial and temporal resolutions and in numerically simulating a tornado that is more than two orders of magnitude smaller than a supercell storm. The
1. Introduction Significant progress has been made in our understanding of supercell storms through Doppler radar measurements and three-dimensional numerical simulations. However, our knowledge of the dynamics of tornadogenesis in supercell storms is still limited because of difficulties in collecting detailed observational data with good spatial and temporal resolutions and in numerically simulating a tornado that is more than two orders of magnitude smaller than a supercell storm. The
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
1. Introduction The National Oceanic and Atmospheric Administration’s Storm Prediction Center (NOAA SPC) provides a 1–8-day lead-time severe weather forecast, including tornado watches. This severe weather forecast is based on synoptic-scale atmospheric instability [e.g., convective available potential energy (CAPE) and low-level wind shear (LLWS)] from numerical weather forecast models and observations. To extend the current forecast lead time for tornadogenesis to subseasonal time scales (i
1. Introduction The National Oceanic and Atmospheric Administration’s Storm Prediction Center (NOAA SPC) provides a 1–8-day lead-time severe weather forecast, including tornado watches. This severe weather forecast is based on synoptic-scale atmospheric instability [e.g., convective available potential energy (CAPE) and low-level wind shear (LLWS)] from numerical weather forecast models and observations. To extend the current forecast lead time for tornadogenesis to subseasonal time scales (i
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
