Geoscience Reference
In-Depth Information
penetrate the inversion. The convective trigger is
sometimes provided by the approach of a cold
front towards the western edge of the moist
tongue. Tornadoes may also occur in association
with tropical cyclones (see p. 341) and in other
synoptic situations if the necessary vertical
contrast is present in the temperature, moisture
and wind fields.
The exact tornado mechanism is still not fully
understood owing to observational difficulties.
Tornadoes tend to develop in the right-rear
quadrant of a severe thunderstorm. Supercell
thunderstorms are often identifiable in plan view
on a radar reflectivity display by a hook echo
pattern on the right-rear flank (
Plate 9.4
). The
echo represents a (cyclonic or anticyclonic) spiral
cloud band around a small central eye and its
appearance may signal tornado development. The
origin of the hook echo appears to involve the
Low
Low-level
Moist Tongue
Gulf of Mexico
Figure 9.33
The synoptic conditions favoring
severe storms and tornadoes over the Great Plains.
Plate 9.4
A radar image of a hook echo that is often a precursor of tornadic activity.
Source: NOAA NSS 0104.
