Supercells - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 198

Figure 4.22. Idealized illustration of some polarimetric signature in supercells and their loca-
tions within the storm. (Top left) Hail (to be discussed), Z DR arc, and tornado debris signatures
(TDS) at low levels. (Top right) Lemon and Doswell conceptual model of main updrafts and
downdrafts in a supercell (see Figure 4.15, top panel); (bottom) Z DR and K DP columns and
rings at mid-levels; gray outline shows the location of the low-level 35 dBZ contour (from
Kumjian and Ryzhkov, 2008).
The flanking line, a band of convective clouds adjacent to the tallest cloud
towers which are associated with the main updraft, is often present along the rear-
flank gust front. Since the cloud surface on the downshear side (i.e., in the
direction of a vector that represents the difference between the wind vector at an
altitude above and the wind vector at an altitude below) of the storm often
appears smooth ( Figure 4.23 ), it is inferred that the air is stable with respect to
lifting by a finite upward displacement (the cloud surface would otherwise appear
bubbly, more like the surface of a cauliflower; see also Figures 3.12 and 3.39a ).
The U-shaped updraft is sometimes associated with a deep convergence zone
(DCZ) that extends upward to 3 km or so ( Figure 4.24 ). Towers in the flanking
line are forced by updrafts in the DCZ. The DCZ will be looked at in slightly
more depth in Section 4.6.