There's a "three-headed dog" savaging Australia's climate, according to CSIRO scientist Dr Wenju Cai, and two of the heads are eating away at rainfall in southern Australia. The three climate influences referred to by Dr Cai are El Nino, the Southern Annullar Mode, and the Indian Ocean Dipole. All are driven by ocean temperatures, and all are being intensified, to Australia's disadvantage, by global warming.
El Nino, driven by temperatures in the Pacific Ocean, is well studied and has had fairly predictable consequences for mid-latitude eastern Australia. The other two influences are less well known, but Dr Cai said there is growing evidence that their fluxes are behind the drying-out of southern Australia.
One, Southern Annular Mode (SAM), appears to be driving rain-bearing winter fronts progressively out into the Southern Ocean. To the west, the Indian Ocean Dipole (IOD) is blocking the generation of moisture-rich air that crosses the continent to bring Victoria, South Australia and southern NSW vital spring rains.
Dr Cai, a principal research scientist with CSIRO Marine and Atmospheric Research, believes that it's the IOD that is behind the failed spring rains currently causing stress to farmers in the south-east. In a "good" year, the eastern Indian Ocean lying off Western Australia is warmer than the ocean off Africa. The warmth produces convection, and humid pressure systems that stream across to south-eastern Australia where, on meeting cold air from the south, they produce rain. When the eastern Indian Ocean is cool, convection dies away and south-eastern Australia (mainly Victoria and South Australia) can expect less spring rain.
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http://nqr.farmonline.com.au/news/state/agribusiness-and-general/general/climates-threeheaded-dog/1334547.aspx
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