AUSTRALIA: Observation system in the Indian Ocean could improve regional climate prediction

Australian scientists have discovered currents in the Indian Ocean similar to those associated with the El Niño weather pattern in the Pacific. Now the scientists are assessing a possible Indian Ocean climate observation system similar to the system which predicted massive changes in ocean conditions leading up to the last major El Niño in 1997.

An array of 70 moorings across the Pacific Ocean was developed in the 1980’s to report surface meteorology and subsurface temperatures by satellite. This equatorial Pacific array provided advance warning of ocean temperature changes in the western Pacific enabling scientists to predict El Nino conditions months in advance.

“International scientific effort will be devoted over the next five years to finding whether similar predictability can be extracted from the Indian Ocean,” says Senior Australian climatologist, Dr Nan Bray.

Ocean data collection will be greatly enhanced by deep ocean-profiling floats in the Indian Ocean north-west of Australia.

The floats will be used to measure currents in the Indian Ocean. These have been found to be associated with a basin-wide shift in sea temperatures, winds and rain. This phenomenon – known as the Indian Ocean Dipole – affects the frequency of occurrence of certain storm systems.

“We think the Indian Ocean effects are predictable because ocean currents are involved, and currents are more predictable than weather,” says Dr Bray. “Improved climate prediction for the nations around the Indian Ocean would impact on the lives of almost two thirds of the world’s population.”

Dr Bray says the Indian Ocean is associated with the monsoon system while the western tropics of the Pacific Ocean are strongly coupled to the ENSO climate phenomenon.

The storm systems associated with Indian Ocean Dipole were discovered in 1999. These storm events begin on the equator south of India, move rapidly eastward and then split west of Sumatra with one band moving north to bring rain to India while the other storm system moves south to die in the southern Indian Ocean after about five days.

“An examination of the links between these southward-moving storms and Australian rain shows strong rainfall over much of eastern Australia, and also over southwestern Australia, says Dr Bray.

“Furthermore, the frequency of storm events is controlled by the Dipole. There are fewer storms when the dipole generates colder than normal waters north of Australia,” she says.