Search Results
-type supercells in certain environments. Early explanations of this phenomenon included the presence of multiple tornadoes rotating around a single mesocyclone ( Snow and Agee 1975 ; Agee et al. 1976 ), thereby producing the familiar cycloidal damage paths associated with tornado families (e.g., Forbes 1975 ). Lemon and Doswell (1979) used radar, aircraft, and visual observations to develop a conceptual model of mesocyclone/updraft evolution. They suggested that cyclic tornadogenesis results from the
-type supercells in certain environments. Early explanations of this phenomenon included the presence of multiple tornadoes rotating around a single mesocyclone ( Snow and Agee 1975 ; Agee et al. 1976 ), thereby producing the familiar cycloidal damage paths associated with tornado families (e.g., Forbes 1975 ). Lemon and Doswell (1979) used radar, aircraft, and visual observations to develop a conceptual model of mesocyclone/updraft evolution. They suggested that cyclic tornadogenesis results from the
tornadoes/mesocyclones, we would like to point out some qualitative features that we feel are relevant. First, extremely close-range observations of a tornado by Bluestein et al. (2003a) revealed an elliptical structure to the eye, but one that did not appear to rotate. They speculated that deformation was the likely reason for these observations. Bluestein et al. (2003b) found that tornadogenesis was associated with the arrival of a jet of convergence to a cold pool boundary that possessed vortices
tornadoes/mesocyclones, we would like to point out some qualitative features that we feel are relevant. First, extremely close-range observations of a tornado by Bluestein et al. (2003a) revealed an elliptical structure to the eye, but one that did not appear to rotate. They speculated that deformation was the likely reason for these observations. Bluestein et al. (2003b) found that tornadogenesis was associated with the arrival of a jet of convergence to a cold pool boundary that possessed vortices
ground. In a subsequent article, we will address the origins of vorticity and processes linked to tornadogenesis in these storms. b. Parcels with large vertical velocities Time series for groups of parcels that, at a single subjectively chosen “peak time” targeting a strong updraft in each run, all exceed 30 m s −1 upward velocity (50 m s −1 for the high-CAPE case) are shown in Fig. 14 . In environments with reduced CAPE, parcel buoyancy can be expected to contribute less to updraft speeds, as in
ground. In a subsequent article, we will address the origins of vorticity and processes linked to tornadogenesis in these storms. b. Parcels with large vertical velocities Time series for groups of parcels that, at a single subjectively chosen “peak time” targeting a strong updraft in each run, all exceed 30 m s −1 upward velocity (50 m s −1 for the high-CAPE case) are shown in Fig. 14 . In environments with reduced CAPE, parcel buoyancy can be expected to contribute less to updraft speeds, as in
, a = 2 km, and b = 1 km. Unlike the high-resolution simulations of nonsupercell tornadogenesis by LW97a , lobe and cleft instabilities, which in their simulations were important for triggering HSIs, do not occur along the leading edge in any of the present simulations. This is because the leading edge lacks a marked nose structure due to the use of a relatively weak surface friction and a relatively coarse horizontal model resolution. 1) Stably stratified cases Figure 7 shows the horizontal
, a = 2 km, and b = 1 km. Unlike the high-resolution simulations of nonsupercell tornadogenesis by LW97a , lobe and cleft instabilities, which in their simulations were important for triggering HSIs, do not occur along the leading edge in any of the present simulations. This is because the leading edge lacks a marked nose structure due to the use of a relatively weak surface friction and a relatively coarse horizontal model resolution. 1) Stably stratified cases Figure 7 shows the horizontal
Bassett, Nebraska, on 5 June 1999. Part I: Tornadogenesis. Mon. Wea. Rev. , 131 , 2954 – 2967 . Brandes , E A. , 1978 : Mesocyclone evolution and tornadogenesis: Some observations. Mon. Wea. Rev. , 106 , 995 – 1011 . Brandes , E A. , 1981 : Finestructure of the Del City–Edmond tornado mesocirculation. Mon. Wea. Rev. , 109 , 635 – 647 . Brown , R A. , L R. Lemon , and D W. Burgess , 1978 : Tornado detection by pulsed Doppler radar. Mon. Wea. Rev. , 106 , 29 – 38
Bassett, Nebraska, on 5 June 1999. Part I: Tornadogenesis. Mon. Wea. Rev. , 131 , 2954 – 2967 . Brandes , E A. , 1978 : Mesocyclone evolution and tornadogenesis: Some observations. Mon. Wea. Rev. , 106 , 995 – 1011 . Brandes , E A. , 1981 : Finestructure of the Del City–Edmond tornado mesocirculation. Mon. Wea. Rev. , 109 , 635 – 647 . Brown , R A. , L R. Lemon , and D W. Burgess , 1978 : Tornado detection by pulsed Doppler radar. Mon. Wea. Rev. , 106 , 29 – 38
. REFERENCESAndrt, J. C., and M. Lesieur, 1977: Influence of helicity on the evo lution of isotropic turbulence at high Reynolds number. J. Fluid Mech., 81, 187-207.Barnes, S. L., 1978: Oklahoma thunderstorms on 29-30 April 1970. Part I: Morphology ofa tornadic storm. Mon. Wea. Rev., 106, 673-684.Brandes, E. A., 1978: Mesocyclone evolution and tornadogenesis: Some observations. Mort. Wea. Rev., 106, 995-1011.--, 1981: Finestructure of the Del City-Edmond tornadic mesocirculation. Mon. Wea. Rev., !09
. REFERENCESAndrt, J. C., and M. Lesieur, 1977: Influence of helicity on the evo lution of isotropic turbulence at high Reynolds number. J. Fluid Mech., 81, 187-207.Barnes, S. L., 1978: Oklahoma thunderstorms on 29-30 April 1970. Part I: Morphology ofa tornadic storm. Mon. Wea. Rev., 106, 673-684.Brandes, E. A., 1978: Mesocyclone evolution and tornadogenesis: Some observations. Mort. Wea. Rev., 106, 995-1011.--, 1981: Finestructure of the Del City-Edmond tornadic mesocirculation. Mon. Wea. Rev., !09
. Pollution can lead to important changes in the cold pools produced by storms (e.g., van den Heever and Cotton 2007 ) and appear to even have a role in determining storm organization and the possibility of tornadogenesis (e.g., Lerach et al. 2008 ; Snook and Xue 2008 ). Both modeling and observational studies have been used to examine the effects of increased CCN concentrations in warm clouds. Each method has its own advantages and disadvantages. For example, idealized modeling studies can be used to
. Pollution can lead to important changes in the cold pools produced by storms (e.g., van den Heever and Cotton 2007 ) and appear to even have a role in determining storm organization and the possibility of tornadogenesis (e.g., Lerach et al. 2008 ; Snook and Xue 2008 ). Both modeling and observational studies have been used to examine the effects of increased CCN concentrations in warm clouds. Each method has its own advantages and disadvantages. For example, idealized modeling studies can be used to
VOL. 46, No. 14 FIG. 1 la. Trajectories of parcels arriving at radius of 30 cm and aheight of 40 cm. The + indicates the ending point. Each dot indicatesa crossing of height levels which are multiples of five (i.e., z = 5, 10,etc.). Closely bunched dots therefore indicate rapid upward movement.of the significance of this experiment to the tornadogenesis problem. We first consider the case when the vanes are parallelat all levels, so that, Upon neglecting boundary effects,potential flow is
VOL. 46, No. 14 FIG. 1 la. Trajectories of parcels arriving at radius of 30 cm and aheight of 40 cm. The + indicates the ending point. Each dot indicatesa crossing of height levels which are multiples of five (i.e., z = 5, 10,etc.). Closely bunched dots therefore indicate rapid upward movement.of the significance of this experiment to the tornadogenesis problem. We first consider the case when the vanes are parallelat all levels, so that, Upon neglecting boundary effects,potential flow is
tornadogenesis. While they calculated the circulation using a line integral, we calculated the circulation using an area integral of vorticity over a material surface (MS), which has an advantage of giving additional information about how tilting and stretching of vorticity take place. The next section describes a numerical simulation of DDVs in a convective mixed layer, performed at a very fine resolution. Section 3 describes results of the backward-trajectory analysis on the circulation. The results are
tornadogenesis. While they calculated the circulation using a line integral, we calculated the circulation using an area integral of vorticity over a material surface (MS), which has an advantage of giving additional information about how tilting and stretching of vorticity take place. The next section describes a numerical simulation of DDVs in a convective mixed layer, performed at a very fine resolution. Section 3 describes results of the backward-trajectory analysis on the circulation. The results are
by the entire radar network, the updraft, reflectivity, and vorticity evolution through the tornadic phase nearly paralleledthat of the Del City storm.' Further understahding of these storms and theirinteraction is developed in other studies. In one related study, Brandes (1981) discusses tornadogenesis around the time of tornado occurrence for one ofthe storms investigated here (Del City). Johnsonet al. (1980)7 present a preliminary overview of thestorm discussed in this paper. Johnson et al
by the entire radar network, the updraft, reflectivity, and vorticity evolution through the tornadic phase nearly paralleledthat of the Del City storm.' Further understahding of these storms and theirinteraction is developed in other studies. In one related study, Brandes (1981) discusses tornadogenesis around the time of tornado occurrence for one ofthe storms investigated here (Del City). Johnsonet al. (1980)7 present a preliminary overview of thestorm discussed in this paper. Johnson et al
