Fresh Science

Ocean unlocks more clues to Australia’s climate as El Nino goes walkabout – Scott Power.

Scott’s new research shows that a long term fluctuation in the Pacific’s temperature can have a profound influence on El Nino and La Nina.

AUSTRALIA’S climate, and notably its rainfall, is influenced by year-to-year variations in sea surface temperatures in the tropical Pacific Ocean. At opposite ends of the spectrum lie El Niño – associated with drought in Australia – and La Niña – associated with floods in Australia.

But research led by Dr Scott Power in the Bureau of Meteorology Research Centre (BMRC) and the Co-operative Research Centre for Southern Hemisphere Meteorology (CRC)* has shown that another cycle of rising and falling sea surface temperatures in the Pacific Ocean – a longer-term, so-called Inter-decadal Pacific Oscillation (IPO) – is also acting in the background to influence Australia’s rainfall and temperature. The project was recently described at ScienceNOW! held in Melbourne on May 6-9 along with another 15 new and exciting research projects.

While El Niño and La Niña are generally year-to-year events, the IPO has been shown to last decades – 10, 20 or even 30 years. The cause of the phenomenon is not entirely clear, but it is thought by some scientists to involve changes in the heat transported by slow moving, large-scale ocean currents in the Pacific Ocean.

Research due to be published in May in ‘Climate Dynamics’ by the Bureau and the CRC (in conjunction with the United Kingdom Meteorological Office and NASA in the United States)** has shown that when the IPO warms the central Pacific, the impact of El Niño and La Niña on Australia appears to wane. This helps to explain the long-standing mystery as to why an El Niño or La Niña event does not always have a profound influence on Australia’s climate. Conversely, when the IPO cools the central Pacific, El Niño and La Niña events have a stronger influence on Australian climate – its rainfall, temperature, and even wheat crop yield.

The IPO appears to not only modulate the impact that El Niño and La Niña have on Australia – it also appears to modulate the strength and vigour of the El Niño and La Niña events directly. So these results have implications for climate prediction in other countries.

The findings may eventually affect the way in which the Bureau’s National Climate Centre produces its three-month outlook for rain over the entire continent – the seasonal climate outlook. The outlook has been issued each month for a decade and proves useful to a wide range of Australians, including farmers.

The Bureau is also working with the CRC, LWRRDC, the CSIRO and Queensland research institutes on long-term projects to see if this information can benefit on-farm decision making.

It is also expected that the influence of the IPO will be implicitly included in the Bureau’s global coupled atmosphere-ocean model of the earth’s climate. The model is now being developed as an experimental seasonal forecasting system.

For now though, the National Climate Centre’s seasonal climate outlook is based on variations in sea-surface temperatures in the Pacific and Indian oceans, and the inclusion in October last year of Indian Ocean temperatures is expected to partially offset any reduction in forecast skill which might occur when the IPO is in its warmer phase.

* S.Power, F.Tseitkin, V.Mehta, B.Lavery, S.Torok and N. Holbrook. (1999) Decadal Climate Variability in Australia during the 20th Century. Bureau of Meteorology Research Centre Research Report No.67.

Power, S, Tseitkin, F., Colman, R., and A. Sulaiman, 1998: A coupled general circulation model for seasonal prediction and climate change research. BMRC Research Report No. 66, 52pp.

** S.Power, T. Casey, Bureau of Meteorology Research Centre, Melbourne,

Australia, (S. Power is also member of the Cooperative Research Centre for Southern Hemisphere Meteorology, Monash University, Clayton, Victoria, Australia, and is now at the

National Climate Centre, Bureau of Meteorology, Melbourne, Australia) C. Folland and A. Colman, Hadley Centre for Climate Prediction and Research, Meteorological Office, Bracknell, Berkshire, UK, and V. Mehta, Joint Centre for Earth System Science, University of Maryland/NASA Goddard Space Flight Centre, MD, USA. (May 1999). Inter-decadal Modulation of the Impact of ENSO on Australia. Climate Dynamics, (to appear).

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