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. Stage 1: Mesocyclonic rotation The first stage of the supercell tornadogenesis process is necessarily the development of a rotating updraft and with that a supercell’s defining feature: the mesocyclone . How an updraft acquires this mesocyclonic rotation is far and away the most well-understood component of the multistep tornadogenesis process. Seminal work by Rotunno (1981) , Lilly (1982) , and Davies-Jones (1984) showed how horizontal vorticity (rotation along a horizontal axis; see green
. Stage 1: Mesocyclonic rotation The first stage of the supercell tornadogenesis process is necessarily the development of a rotating updraft and with that a supercell’s defining feature: the mesocyclone . How an updraft acquires this mesocyclonic rotation is far and away the most well-understood component of the multistep tornadogenesis process. Seminal work by Rotunno (1981) , Lilly (1982) , and Davies-Jones (1984) showed how horizontal vorticity (rotation along a horizontal axis; see green
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
terrain of the Rocky Mountains, and vertical wind shear) are closely tied to the pole-to-equator thermal gradients, but the mere presence of those gradients on the synoptic scale is no guarantee that these ingredients will be brought together to produce tornadoes in any specific extratropical cyclone. Horizontal temperature gradients also exist on the storm scale. Temperature gradients associated with downdrafts and outflow are likely important in tornadogenesis in supercells (the most violent
terrain of the Rocky Mountains, and vertical wind shear) are closely tied to the pole-to-equator thermal gradients, but the mere presence of those gradients on the synoptic scale is no guarantee that these ingredients will be brought together to produce tornadoes in any specific extratropical cyclone. Horizontal temperature gradients also exist on the storm scale. Temperature gradients associated with downdrafts and outflow are likely important in tornadogenesis in supercells (the most violent
prediction of QLCS tornadogenesis is identifying when and where along the QLCS tornadoes will occur (e.g., Ashley et al. 2019 ; Lovell and Parker 2022 ). In response, considerable operational attention has been given to the “three-ingredients method” ( Schaumann and Przybylinski 2012 ) to locally access QLCS mesovortexgenesis and, correspondingly, tornadogenesis potential, but there is uncertainty in thresholds, broad applicability, and the optimal combination of parameters (e.g., Gibbs 2021 ; Ungar
prediction of QLCS tornadogenesis is identifying when and where along the QLCS tornadoes will occur (e.g., Ashley et al. 2019 ; Lovell and Parker 2022 ). In response, considerable operational attention has been given to the “three-ingredients method” ( Schaumann and Przybylinski 2012 ) to locally access QLCS mesovortexgenesis and, correspondingly, tornadogenesis potential, but there is uncertainty in thresholds, broad applicability, and the optimal combination of parameters (e.g., Gibbs 2021 ; Ungar
VORTEX2 is the largest, most ambitious study focused on improving our understanding of tornadoes, including tornadogenesis, tornado structure, and improving forecasts. Nearly all of the most intense tornadoes, those capable of causing the most widespread damage and largest number of fatalities, are spawned by supercell thunderstorms. Recently, computer models and observing technology used to study supercells have become more accessible and increasingly sophisticated, enabling detailed
VORTEX2 is the largest, most ambitious study focused on improving our understanding of tornadoes, including tornadogenesis, tornado structure, and improving forecasts. Nearly all of the most intense tornadoes, those capable of causing the most widespread damage and largest number of fatalities, are spawned by supercell thunderstorms. Recently, computer models and observing technology used to study supercells have become more accessible and increasingly sophisticated, enabling detailed
(VORTEX2) ( Wurman et al. 2012 ), have provided insight into these processes, but forecasting tornadogenesis within an already-formed supercell remains a formidable challenge. Seminal numerical simulations of supercell thunderstorms conducted in the 1970s and 1980s (e.g., Klemp and Wilhelmson 1978a , b ; Schlesinger 1980 ; Rotunno and Klemp 1982 ; Weisman and Klemp 1982 , 1984 ; Rotunno and Klemp 1985 ) were the basis from which scientific theories of supercell formation, strength, and
(VORTEX2) ( Wurman et al. 2012 ), have provided insight into these processes, but forecasting tornadogenesis within an already-formed supercell remains a formidable challenge. Seminal numerical simulations of supercell thunderstorms conducted in the 1970s and 1980s (e.g., Klemp and Wilhelmson 1978a , b ; Schlesinger 1980 ; Rotunno and Klemp 1982 ; Weisman and Klemp 1982 , 1984 ; Rotunno and Klemp 1985 ) were the basis from which scientific theories of supercell formation, strength, and
mesocyclone from Guangzhou and Shenzhen radars at (a)–(c) 1.5- and (d)–(f) 3.5-km heights for before [(a),(d) 1430 and (b),(e) 1454 LST] and at the time of [(c),(f) 1530 LST] tornadogenesis. Reflectivity (color; dB Z ) is overlaid with storm-relative wind vectors. The positive (white solid contours) and negative (white dashed contours) vertical vorticity is shown at ±1, 5, 10, 15, and 20 × 10 −3 s −1 . The updraft (blue line) is contoured at 2, 4, 6, 8, and 10 m s −1 . The green-filled triangles in (c
mesocyclone from Guangzhou and Shenzhen radars at (a)–(c) 1.5- and (d)–(f) 3.5-km heights for before [(a),(d) 1430 and (b),(e) 1454 LST] and at the time of [(c),(f) 1530 LST] tornadogenesis. Reflectivity (color; dB Z ) is overlaid with storm-relative wind vectors. The positive (white solid contours) and negative (white dashed contours) vertical vorticity is shown at ±1, 5, 10, 15, and 20 × 10 −3 s −1 . The updraft (blue line) is contoured at 2, 4, 6, 8, and 10 m s −1 . The green-filled triangles in (c
chosen for analysis. The radar reflectivity and copolar cross-correlation coefficient were objectively analyzed to a Cartesian grid using a two-pass Barnes filter ( Koch et al. 1983 ). The filter and grid parameters were chosen based on the data resolution δ at the range of the tornado. The KTLX data are oversampled every 0.5° in azimuth. The range from the radar to the tornado varied from 30.6 km at 1955:27 UTC (near the time of tornadogenesis; hereafter all times are UTC) to 11.9 km at 2033
chosen for analysis. The radar reflectivity and copolar cross-correlation coefficient were objectively analyzed to a Cartesian grid using a two-pass Barnes filter ( Koch et al. 1983 ). The filter and grid parameters were chosen based on the data resolution δ at the range of the tornado. The KTLX data are oversampled every 0.5° in azimuth. The range from the radar to the tornado varied from 30.6 km at 1955:27 UTC (near the time of tornadogenesis; hereafter all times are UTC) to 11.9 km at 2033
The most extensive published guidelines to carrying out studies of tornadoes were written by Johannes Letzmann and Harald Koschmieder, issued in 1937. Forgotten for decades, they are presented here in translation, accompanied by commentary and background material. They provide insight into the development of concepts of tornadogenesis, and a measure of the progress made in tornado research in the recent past.
The most extensive published guidelines to carrying out studies of tornadoes were written by Johannes Letzmann and Harald Koschmieder, issued in 1937. Forgotten for decades, they are presented here in translation, accompanied by commentary and background material. They provide insight into the development of concepts of tornadogenesis, and a measure of the progress made in tornado research in the recent past.
This paper describes the Verification of the Origins of Rotation in Tornadoes Experiment planned for 1994 and 1995 to evaluate a set of hypotheses pertaining to tornadogenesis and tornado dynamics. Observations of state variables will be obtained from five mobile mesonet vehicles, four mobile ballooning laboratories, three movie photography teams, portable Doppler radar teams, two in situ tornado instruments deployment teams, and the T-28 and National Atmospheric and Oceanic Administration P-3 aircraft. In addition, extensive use will be made of the new generation of observing systems, including the WSR-88D Doppler radars, demonstration wind profiler network, and National Weather Service rawinsondes.
This paper describes the Verification of the Origins of Rotation in Tornadoes Experiment planned for 1994 and 1995 to evaluate a set of hypotheses pertaining to tornadogenesis and tornado dynamics. Observations of state variables will be obtained from five mobile mesonet vehicles, four mobile ballooning laboratories, three movie photography teams, portable Doppler radar teams, two in situ tornado instruments deployment teams, and the T-28 and National Atmospheric and Oceanic Administration P-3 aircraft. In addition, extensive use will be made of the new generation of observing systems, including the WSR-88D Doppler radars, demonstration wind profiler network, and National Weather Service rawinsondes.
