Geoscience Reference
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Figure 6.39. Idealized illustration of how counter-rotating vortices (anticyclonic member A,
cyclonic member C) can form in a supercell at the ends of an updraft associated with the
flanking line and main updraft. Horizontal cross-section shows solid line enclosing an area of
updraft (U); dashed line encloses a region of downdraft (D). Red line with arrow shows
vorticity streamline (vortex line). Curved red lines with arrows indicate sense of rotation.
(Top) Tilting at the ends of the updraft of horizontal vorticity generated baroclinically near
the flanking line updraft and main updraft, at the edge of the rear-flank downdraft cold pool, if
there is one. (Bottom) Tilting of horizontal vorticity from the environment at the edge of the
rear-flank downdraft and between the rear-flank downdraft and main updraft. In the top case,
the vortex line is arched upward by the updraft; in the bottom the vortex line is arched
downward. In the top illustration, the vortex line may curve back around the other side of
the cold downdraft to form a vortex ring (not shown).
6.6 VORTEX DYNAMICS
The problems of what determines the character of the wind field in a tornado and
what determines whether or not a tornado will form have been addressed using
laboratory models of vortices and numerical models of vortices under highly
idealized, controlled, laboratory model-like conditions. While these idealized
models do not include the effects of external convective storm features producing
and interacting with the vortex and translating along it and do not include the
asymmetric effects present in nature, such as the advection of cooler/warmer and
moister/drier air in specific quadrants of the vortex, they have been very useful in
elucidating many of the observed characteristics of tornadoes in nature.
Axisymmetric, tornado-like vortices in laboratory models (or ''simulators'')
are driven from above by an exhaust fan ( Figure 6.40 ); air is drawn into a rotating
lower section with vanes that channel flow so that some of the airflow is in
 
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