Supercells - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 218

Figure 4.35. Schematic representation of the splitting process in a unidirectionally sheared
environment. Unidirectional shear is indicated at the left. Vertical forces indicated by thick,
shaded arrows; upward forces are dynamic, perturbation pressure gradient forces associated
with mid-level vortices; downward force is due to precipitation loading. Storm-relative airflow
is indicated by cylindrical arrows. Cyclonic ( þ ) and anticyclonic ( ) vortices are produced at
mid-levels. Lines denote vortex lines, which point toward the right, indicating vorticity in the
northerly direction, associated with vertical shear. Vertical dashed lines indicate precipitation.
Cold front symbol at the ground indicates the leading edge of a cold pool. (Top) An updraft
creates counter-rotating vortices, each of which is associated with an upward-directed force
that triggers new updrafts on either side of the westerly vertical shear vector. (Bottom) New
updrafts in turn produce new, mirror image, cyclonic-anticyclonic couplets, and so on (from
Klemp, 1987).