A shimmering featureless tract of the Indian Ocean the size of Sydney Harbour is getting the full attention of CSIRO climate scientists this month.

"We are treating the area, about 300 nautical miles west of Sumatra on the equator, as a rain gauge for Australia's climate," says oceanographer Dr Stuart Godfrey, one of the project leaders.

"We need to know how much rain falls in this area because storms in the region reach up high into the atmosphere, creating upper atmospheric waves that affect weather all around the world.

"The strength of these waves depends on how much rain falls. Satellites give us rain rate estimates, but they aren't very accurate," says Dr Godfrey.

"The best rain gauge may be the ocean itself - checking how its salinity changes with rainfall to affect evaporation."

Dr Godfrey says scientists have confirmed links between rainfall over much of Australia and sea surface temperatures in the Pacific Ocean and the Indian Ocean in the Indonesian region. While the factors which control Pacific Ocean sea surface temperatures are well understood, those affecting the Indian Ocean/Indonesian region sea surface temperatures are not.

"When this upper atmospheric wave generation is stronger over the eastern Indian Ocean, La Nina conditions prevail, providing good rainfall across Australia.

"Alternately, when the region of intense storm activity moves eastward into the Pacific, we have El Nino conditions that can bring on drought," Dr Godfrey says.

"Understanding the processes which influence variations in rainfall, such as the cooler or warmer sea surface temperatures, is also vital for their reading of Greenhouse warming," he says.

The scientific challenge is to investigate the fine balances affecting heat and fresh water and links to the movement of atmospheric storms.

"Essentially, we are checking whether our estimates of the amount of heat going into the ocean is balanced by the change in ocean heat content.

"This time we also want to check whether our estimates of rain and evaporation match the observed changes in water salinity."

Australia's oceanographic research vessel, the RV Franklin, will be the platform for the August 14 to September 11 project, involving CSIRO's Divisions of Oceanography, Atmospheric Research and Environmental Mechanics and the Flinders Institute of Atmospheric and Marines Sciences.

Dr Godfrey says the ship will be bristling with instruments to measure the exchange of heat between the top 150 metres of the ocean and the atmosphere at the surface. Scientists also will take frequent temperature and salinity measurements, while also measuring solar radiation, evaporation, rainfall, and other exchanges across the ocean surface.

"The difficulty in making these measurements accurately enough and often enough has been a major limitation to our capacity to test models of climate in the short and long-term", Dr Godfrey says.

More information from: Dr Stuart Godfrey 002-325210 or Craig Macauley 002-325219