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Subject : L2) Why do tropical cyclones spawn tornadoes?
Contributed by Bill McCaul
Tropical cyclones spawn tornadoes when certain instability and
vertical shear criteria are met, in a manner similar to other
tornado-producing systems. However, in tropical cyclones, the
vertical structure of the atmosphere differs somewhat from that
most often seen in midlatitude systems. In particular, most of
the thermal instability is found near or below 10,000 feet altitude,
in contrast to midlatitude systems, where the instability maximizes
typically above 20,000 feet. Because the instability in TC's is
focussed at low altitudes, the storm cells tend to be smaller and
shallower than those usually found in most severe midlatitude
systems. But because the vertical shear in TC's is also very strong
at low altitudes, the combination of instability and shear can become
favorable for the production of small supercell storms, which have
an enhanced likelihood of spawning tornadoes compared to ordinary
thunderstorm cells (Novlan and Gray
1974, Gentry 1983,
McCaul 1991).
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