Tornadoes - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 355

Figure 6.37. Cyclic tornadogenesis. (Top left) Conceptual model from Burgess et al. (1982) for
a succession of parent mesocyclones; (top right) refined conceptual model from Dowell and
Bluestein (2002). In left panel, numbered circles identify vortices and thick lines indicate wind-
shift lines. Tornado tracks are shaded. In the inserts on the three panels to the right the shaded
area indicates the updraft and the spotted area indicates the downdraft; dashed outlines
indicate regions of production of cyclonic vertical vorticity by tilting of horizontal vorticity,
solid outlines indicate the stretching of vertical vorticity. The arrows denote vortex-relative
trajectories. The time between successive tornadoes is about 20min. (Bottom) Two tornadoes
in the northern Texas Panhandle on May 7, 1986; the thin one to the left is the previous tornado
in a series about to dissipate, the wider one to the right is the next in a series, near its mature
stage (photo by the author).