Geoscience Reference
In-Depth Information
Figure 10.33
Main climatological fea-
tures of Australasia and the southwest
Pacific. Areas with >100 mm (January)
and >50 mm (July) mean monthly pre-
cipitation for Australia are also shown.
Source
: After Steiner, from Salinger
et al
.
(1995), copyright © John Wiley & Sons Ltd.
Reproduced with permission.
by the continual passage of depressions and ridges of
higher pressure. Throughout the Southern Ocean, this
belt extends southward from about 30°S in July and
40°S in January (see Figures 9.18 and 10.35B) to the
Antarctic trough which fluctuates between 60° and
72°S. The Antarctic trough is a region of cyclonic
stagnation and decay that tends to be located furthest
south at the equinoxes. Around New Zealand, the west-
erly airflow at an elevation of 3 to 15 km in the belt 20
to 50°S persists throughout the year. It becomes a jet
stream at 150 mb (13.5 km), over 25 to 30°S, with a
velocity of 60 ms
-1
in May to August, decreasing to 26
ms
-1
westerlies depends on the meridional pressure differ-
ence between 40 and 60°S, being on average greatest
all the year south of western Australia and west of
southern Chile.
Many depressions form as waves on the inter-
anticyclonic fronts, which move southeastward into the
belt of the westerlies. Others form in the westerlies at
preferred locations such as south of Cape Horn, and
at around 45°S in the Indian Ocean in summer and in the
South Atlantic off the South American coast and around
50°S in the Indian Ocean in winter. The polar front
(see Figure 9.20) is associated most closely with the
sea-surface temperature gradient across the Antarctic
in February. In the Pacific, the strength of the
