Supercells - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 207

Figure 4.28. Idealized representation of a horizontal cross section at low levels of features in
(top) an LP supercell, (middle) a classic supercell, and (bottom) an HP supercell. Dashed line
encloses hail and heavy rain. The region under the updraft base is translucent, as is much of the
storm, in an LP supercell. The region under the updraft base shows a limited precipitation shaft
and is partially translucent in a classic supercell. The region under the updraft base is opaque in
an HP supercell and precipitation has wrapped almost or all the way around the tip of the
updraft, where a tornado might be found, but mostly hidden from view, except perhaps in the
notch just ahead of the nose of the updraft, which is not a safe place to be (after Rasmussen and
Straka, 1998).

cyclonic (vertical) vorticity and some is converted into anticyclonic (vertical)
vorticity as a result of tilting (cf. (2.50)) along the edges of the updraft, in a direc-
tion with respect to the updraft that is normal to the shear vector. We first
consider, for simplicity, an atmosphere in which the shear profile (i.e., vertical
variation of shear) is unidirectional (shear does not change direction with height)
and is constant (shear magnitude does not vary with height). For westerly wind
shear, which according to the thermal wind relationship (4.23) is associated with a
north to south-directed temperature gradient (cold to the north, warm to the
south), a cyclonic vortex will form on the equatorward side of the updraft and an
anticyclonic vortex will form on the poleward side.
Analysis of the production of mid-level rotation may also be easily visualized
using ''vortex line'' analysis. Consider the frictionless form of the three-