East Asia and Western Pacific METEOROLOGY AND CLIMATE

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2100 GMT 9 MAY 5 104 J03 IO2 101 100 99 98
LONGITUDE («W)
2.6 An Australian "Southerly Buster"
In the late spring and summer, the southeast coast of New South Wales in Australia often
experiences an intense squall with an abrupt wind change into the south. The squall, which is
associated with a cold front, is sometimes accompanied by severe weather, and can cause loss of
life and property. The event is referred to as the "Southerly Buster."
Although the "Southerly Buster" refers to the narrow (approximately 50 km) squall and
wind shift ahead of the cool southerly current, Howells and Kuo (1988) were able to simulate many
features of the rnesoscale environment of a "Southerly Buster" that occurred on 1 December 1982
using MM4 with 40-km horizontal resolution. The simulated southerly flow was a relatively
shallow and narrow current of cold air. Model sensitivity experiments indicated that orography
and land-sea contrasts played major roles in the production of the observed strong gradients of
temperature and wind in the lower troposphere.
Analysis of the model simulations indicates that the following physical processes
contribute to the development of the environment of the Southerly Busier:
(i) channelling of cool maritime air around the southeastern extent of the mountain
ranges,
(ii) blocking of the flow on the western side of the mountains,
(iii) adiabatic downslope heating of the prefrontal westerly air flow,
(iv) sensible heating of the prefrontal continental air mass,
(v) reduced fractional coupling of the warm prefrontal westerlies over the cooler ocean,
and
(vi) greater friction over land which retards the progress of the front over land compared
to over ocean.
2.7 Appalachian Cold-Air Damming And Coastal Frontogenesis
In the winter and spring when anticyclones are centered over New England, a ridge of high
pressure accompanied by a shallow layer of cold air often extends southward to the east of the
Appalachian Mountains. This persistent cold air is sometimes associated with freezing rain as
warm, moist air from the southwest overruns the stable air mass. A quasi-stationary coastal front
typically separates the cold air over land from the milder air over the oceans. Because of its
shallow nature, the phenomenon has been difficult to predict with operational numerical models.