Geoscience Reference
In-Depth Information
105°E
120°E
135°E
150°E
165°E
IPWP
0°
0°
15°S
15°S
30°S
30°S
105°E
120°E
135°E
150°E
165°E
Figure 22.4. The Indo-Pacific Warm Pool bounded by the 28
°
C isotherm. (After
Williams et al.,
2009b
.)
cyclones and by convectional disturbances at the start and close of the wet season
(Linacre and Hobbs,
1977
). The minimum sea surface temperature (SST) for tropical
cyclone genesis is about 26
C (see
Figure 22.4
), and tropical cyclones can contribute
up to 50 per cent of the annual rainfall in the far north (Gentilli,
1971
). The West
Pacific Warm Pool, shown in
Figure 22.4
, and the poleward flowing warm Leeuwin
Current (
Figure 22.3
) both came into being some 30 million years ago as a result of
Australia's northward drift, which is discussed in
Section 22.4
.
Occasional low-pressure troughs extending from the north-west and north into
southern Australia can bring tropical moisture beyond the monsoon zone during
summer. The arid centre has very hot, dry summers and cold, dry winters, while the
temperate south receives most of its rain in winter, when the westerly air masses
extend furthest to the north. A small area in the south-east is also under the influence
of the south-east Trade Winds in summer, and receives as much rain in summer as it
does in winter.
In order to answer the questions of when, how and why Australia became arid,
we need to know when it attained its present latitudinal position, when the Eastern
Highlands first attained their present elevation and when the cold West Australian
Current was first established.
°
