Australasian Science: Australia's authority on science since 1938

Indian Ocean Dipole Causes Winter Droughts

By Stephen Luntz

The Indian Ocean Dipole has dried southern Australia out, and we can expect more of the same according to Dr Wenju Cai of CSIRO Wealth from Oceans.

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The good news is that understanding of the phenomenon may enable us to predict bushfire seasons.

The Indian Ocean Dipole is based on the relative temperatures of the two ends of the Indian Ocean. When the eastern end is relatively cold and the western end is warm, compared with their long term averages, it is said to be positive while the reverse conditions are described as negative. The weather of surrounding regions is affected just like much of the planet changes in response to El Niño and La Niña events.

However, while El Niños and La Niñas are becoming more intense (AS, Jan/Feb 2014, p.10) there is no evidence of a trend one way or another. The same is not true for the Dipole.

“Over the past 50 years, the Dipole has been trending upwards, increasing the number of positive events, occurring an unprecedented 11 times over the past 30 years,” says Cai. “For example, there were three consecutive positive Dipole events between 2006 and 2008, which preconditioned the catastrophic Black Saturday bushfires in Victoria.”

Cai explains that the Eastern Indian Ocean is historically warmer than its counterpart to the west. This creates a huge convection tower that brings winds in from the west.

However, global warming has seen the troposphere warm faster than the ground, “making the atmosphere more stable” and reducing the inflowing winds. The...

The full text of this article can be purchased from Informit.