The Hindu Business Line : El Nino traced to `variations' in Indian Ocean

LATEST research findings in the US have linked events in the Pacific Ocean, such as the initiation of El Nino episodes, to variations in the East Indian Ocean.

These large organised weather systems may prefer to travel over water affecting certain areas of the Maritime Continent and not others, as per research carried out by a NASA (National Aeronautics and Space Administration)-funded team from East Carolina University in the US.

The team created the El Nino Onset Index (EOI), an index using satellite data of rain and winds in the eastern Indian Ocean that accurately predicted the arrival of the 2002-2003 El Nino.

During the winter of 2001-2002, the climate of the eastern Indian Ocean underwent a dramatic shift as westerly winds increased and the weather flip-flopped from dry to wet.

EOI may not be sensitive enough to register weak episodes, one of which has been evolving in the Pacific waters from early this year.

Also, the current El Nino is not basin-wide, as the far eastern Pacific is cooler than normal. After computing the EOI back to 1979, the only El Nino that the team could not "predict" was the weakest event in 1993.

Based on rain data: The team developed the EOI using the rainfall data alone. This was because the rainfall data was a consistent indicator of an oncoming El Nino, as compared to the wind data. It made use of NASA's Tropical Rainfall Measuring Mission (TRMM) and QuikScat satellite data ranging from November 2001 to March 2002.

The 2002-03 El Nino was the first where TRMM data was available for the entire event. The researchers used satellite data to track two instances of wind, rainfall, and warmer sea surface temperatures moving from the Indian to the Pacific Ocean in early 2002 prior to the 2002-03 El Nino.

The first organised rain event followed the Equator and the second travelled further south closer to Australia. In the latter example, warm waters appeared first, followed by heavy rainfall in the eastern Indian Ocean. Then, strong westerly winds and a cooling of the sea surface developed.

This sequence of events moved through the ocean area between Indonesia and Australia, suggesting a connection between rising air, wind, and sea surface temperatures over a period of days. El Nino is signalled by a warming of the ocean surface off the western coast of South America that occurs every 4 to 12 years when cold, nutrient-rich water does not come up from the ocean bottom. It affects Pacific jet stream winds, altering storm tracks and creating unusual weather patterns in various parts of the world.

NASA uses its Earth observing satellites to also study climate patterns and related conditions. In the future, it proposes to launch the Global Precipitation Measurement Mission, which will contribute to the EOI, as TRMM is doing currently.

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