Tropical Cyclone Motion
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Tropical cyclones move approximately with a suitably
defined vertical vector average o
off the flow in which they
are embedded
2
3
4
35
50
Latitude
30
40
25
30
20
20
15
145
150
155
Longitude
5
160
165
Lagrangian chaos:
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Vortices in PV gradients:
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Baroclinic vortices in shear: A simp
simple model
• Two layers, with
i h zero eff
ffectiive PV gradient,
di
but upper
layer moving with respect to lower layer
• Lower layer contains point potential vortex
vortex, whose
circulation projects outward and upward
• Upper layer has point source of zero PV air co-located
with lower point vortex; zero PV air separated from
surroundings by a single, expanding contour
• Flow owing to upper level PV anomaly solved by contour
dynamics
(From Wu and
(F
dE
Emanuell, 1993)
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Lower (left) and upper (right) flows for zero shear:
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Evolution of upper layer vortex patch when weak shear is
present
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Evolution of upper layer vortex patch when moderate
shear is present
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Evolution of upper layer vortex patch when strong shear
is present
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Operational prediction of tropical cyclone tracks:
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Examp
ple: 20 random tracks passing
g within 100 km of Boston
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20 “worst” tracks:
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