Thursday, 15 August 2002
Characteristics of RUC vertical wind profiles near supercells
Proximity vertical wind profiles obtained from Rapid Update Cycle (RUC) analyses were analyzed near approximately 450
supercells. Supercells were classified as nontornadic, weakly tornadic (associated with F0-F1 tornadoes), and strongly tornadic (associated with F2-F5 tornadoes). The differences between weakly tornadic and nontornadic supercells were relatively small. Wind profiles associated
with strongly tornadic supercells differed significantly from weakly tornadic and nontornadic supercells in only the lowest 1 km, with the vertical wind shear being approximately 70% larger on average in this
layer near strongly tornadic supercells compared to other
supercells. The vertical profiles of streamwise vorticity
and storm-relative helicity density also were significantly different
between strongly tornadic supercell environments and weakly
tornadic/nontornadic supercell environments. Curiously, storm-relative
wind profiles were similar for all supercell classes, whereas
ground-relative winds were roughly 5 m/s larger on average throughout
the troposphere in strongly tornadic supercell environments compared to
those associated with nontornadic supercells. Perhaps the substantially
larger low-level shear in strongly tornadic supercells simply is due to
the presence of larger gradient flow in the free atmosphere, which leads
to larger boundary layer shear due to surface drag. Mean hodographs
also were constructed for the three types of supercell classes. The
hodographs had virtually indistinguishable appearances above 1
km. Given the wind profile similarities aloft, there is little wonder
why operationally discriminating between tornadic and nontornadic
environments has been so difficult. It is believed that it may be
worthwhile to develop new technologies capable of better sampling the
vertical wind profile in the lowest 1000 m, and with much improved
horizontal resolution compared to the current wind profiler
demonstration network. It also is believed that it would be fruitful
for future numerical simulation studies to concentrate on the effects of
hodograph differences in the lowest 1000 m on simulated supercells.
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