Supercells - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 234

4.5.4 Sensitivity of simulated supercell structure to environmental thermodynamic
and cloud microphysics parameters

While the overall behavior of supercells can be explained qualitatively based on
idealized soundings (i.e., on idealized vertical profiles of vertical wind shear and
CAPE), significant differences in storm morphology (e.g., in the degree of surface
cold outflow) and intensity (updraft speed, peak mid-level, and surface vorticity)
are found, especially when CAPE is relatively low. In most supercells in the Great
Plains of the U. S., CAPE is relatively high (

1,500 j kg 1 ) and the level at which
potential buoyancy is highest is around 6-10 km AGL. When CAPE is relatively
low (

>

1,000 j kg 1 ), but is concentrated at low levels, potential buoyancy at low
levels can match shear better (in the sense that R 1 for buoyancy and shear at
low levels); when shear is relatively weak, but is concentrated at low levels, shear
at low levels can match CAPE better at low levels. Thus, supercells can occur that
are relatively shallow, as is observed in landfalling tropical cyclones or the outer
rainbands in tropical cyclones ( Figure 4.48 ) and in some mid-latitude storms
having a cold core aloft and a low tropopause ( Figure 4.49 ). In these storms,
potential buoyancy is highest around 3 km AGL. These relatively shallow
supercells are sometimes called ''mini-supercells'' or ''low-topped supercells''. Like

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Figure 4.48. Supercells in the Gulf of Mexico off the west coast of Florida, in an outer
rainband of Hurricane Ivan on September 15, 2004, as detected by the WSR-88D radar at
Tallahassee, FL.