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Figure 4.21. Idealized illustration of how a supercell that formed in an environment of a
clockwise-turning hodograph with height can lead to the enhancement of differential reflectiv-
ity Z DR along the edge of the FFD on the right-front flank of the storm. The causes of this
polarimetric signature are differential fall speeds in an environment of strongly curved vertical
shear. The largest water drops (thick solid line) fall out (from the common location noted) and
land near the edge of the radar echo (shaded dark gray); the medium-size drops (dashed line)
fall out and land farther inside the radar echo (shaded medium gray); the small drops (dotted
line) fall out and land farthest inside the radar echo (shaded light gray). Since small drops are
''seen'' as a region of relatively small differential reflectivity, while large drops are ''seen'' as a
region of relatively high differential reflectivity, there is a differential reflectivity gradient on the
right-forward flank of supercells at low levels, owing to the vertical shear profile (if hail falls
out, the Z DR arc is disrupted) (from Kumjian et al., 2009).
smallest raindrops are carried farther into the core before falling out than the
larger, more widely spaced raindrops, a size-sorting process that is associated with
both vertical directional and speed shear and vertical velocity ( Figure 4.21 ). A
summary of the prominent polarimetric signatures seen in supercells is shown in
Figure 4.22. (The tornado-debris signature is discussed in Chapter 6, while the
Z DR and K DP rings are not discussed here.)
 
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