Supercells - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 221

Figure 4.36c. As seen visually, in eastern Colorado, on August 16, 2009, with a view to the
east. The storm is about to split in the top image; the middle and bottom images indicate the
RM and LM updraft bases. In the bottom image, precipitation can be seen falling in between
the updraft bases, as in Figure 4.35 (photographs by the author).
discovered, was considered quite exotic and likened to the behavior of biological
mitosis.
In nature, straight (or nearly straight) hodographs are frequently found above
the boundary layer, but not in the boundary layer itself, owing to turbulent
friction. The vertical variation of vertical shear in the well-known Ekman profile
(without baroclinicity) has a marked change in direction with height ( Figure 4.38 ).
Let us now consider how updraft propagation is affected by the linear
pressure term. From (4.46) it was shown ( Fig. 4.34 ) that in the upshear (down-
shear) from an updraft the perturbation pressure is relatively high (low). When
the hodograph is straight and most of the shear is below mid-levels, and when the
updraft speed increases with height, then there is an upward (downward) directed
perturbation pressure gradient force on the downshear (upshear) side. Thus, the