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high p
(a)
cold
low p
warm
high p
(b)
cold
warm
(c)
A
′
A
low
cold
B
′
B
warm
high p
(d)
cool
low
C
′
C
cold
warm
high p
Fig. 3.3
Evolution of a typical extratropical cyclone (in the Northern Hemisphere), as derived from surface
weather maps, with the geostrophic wind velocity vectors shown parallel to the isobars; (a) illustrates
an assumed initial state as a stationary front with wind shear; this interface is unstable and it
gradually develops into a frontal wave with growing amplitude as shown in (b) and (c). In (d) the warm
front has been overtaken by the cold front and the cyclone has become occluded. From then on the
cyclone loses its strength and the fronts gradually dissolve.
