Ordinary-cell convective storms - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 155

Figure 3.48. Illustration of discrete propagation in a multicell convective storm. (Top) PPI
(plan view of ) radar reflectivity factor contours (in dBZ) at various altitudes as a function of
time. The arrow shown in each panel indicates the direction of cell motion. (Bottom) Vertical
cross section of radar reflectivity contours for ''Cell 3'', which is shaded. The stormmotion is to
the northeast and discrete propagation occurs on the right flank of the storm (from Chisholm
and Renick, 1972).

melting layer and cools even more, so that the cold pool deepens or becomes
cooler or both. If D u remains constant, eventually c increases (cf. (3.32)), so that

c u and the RKW condition for optimum growth no longer is met. The ver-

tical circulation at the leading edge of the cold pool then leans rearward with
height ( Figure 3.40, top right), so that new cells propagate rearward with respect
to the leading edge of the gust front (cold pool) and discrete, multicell growth is
possible; the phase shift between growing vertical circulations and the vertical circu-
lation along the leading edge of the cold pool is essential to the process ( Figure
3.51 ). If the shear is increased so that

> D

D u ! c, new-cell growth becomes more

continuous and ''weakly evolving''.

3.4 GENERAL MONOGRAPHS AND TOPICS

The reader is referred to p. 24 for a list of relevant general monographs and
topics.