Indian Ocean has its own El Niño

Storm clouds over the Kalahari desert in southern Africa, as seen from the space shuttle

October 11, 1999
Web posted at: 11:51 a.m. EDT (1551 GMT)

The Indian Ocean has its own El Niņo-like phenomenon and it doesn't always occur at the same time as the El Niņo in the Pacific Ocean, according to researchers trying to better understand how the Indian Ocean affects climate. They hope their research will help improve forecasts for nearby countries and save lives.

"Roughly 65 percent of the world's population lives in monsoon regions," said Peter Webster, director of the University of Colorado at Boulder's Program in Atmospheric and Oceanic Sciences. "This is the fastest growing region on the planet. By the year 2025, it is anticipated this number will grow to 75 percent."

Although the Indian Ocean's summer monsoon was strongly linked to the El Niņo/Southern Oscillation system, or ENSO, from 1960 to 1988, there has been no significant link since that time, said Webster. ENSO triggers movement of warm water from the western Pacific eastward every two to 10 years, wreaking havoc on the environment through the proliferation of droughts and floods worldwide.

"Our research indicates the Indian Ocean has its own El Niņo-like phenomenon characterized by an east to west oscillation of warm waters that affect other parts of the world," said Webster.

The monsoon starts over Southeast Asia in early March and April then moves into South China. By mid-May, cross-equatorial winds grow in association with heavy rainfall on the southern tip of the Indian subcontinent. By June, the monsoon rain has reached East Asia. The concentrated rainfall during the monsoon period, usually no longer than two weeks, is crucial for the agriculture over Asia. Failure of the monsoon often results in devastating drought over China, Japan and Korea.

The Indian Ocean generally has three active periods during the annual summer monsoon and three relatively calm periods, said Webster. As the Indian Ocean heads toward an active period, waves up to 15 feet high replace calm water and the surface water warms significantly. Warm ocean water pumps large amounts of moisture into the atmosphere, creating rainfall over India, East Africa, South Asia and Australia.

The Indian Ocean monsoon triggered the wettest years on record, 1997 and 1998, in East Africa. This set off an outbreak of mosquito-borne Rift Valley Fever and associated cholera and malaria in livestock and people. "This event occurred completely independent of El Niņo activity," said Webster.

"Our goal is to understand the basic physics that underpin these variations in the Indian Ocean monsoons and allow us to predict them so people in the region will have warning weeks or months in advance of drought or floods," he said. "It is the variability on these time scales that really impact agriculture and society, and the annual Indian monsoon is a major player in these climate fluctuations."

The Indian Ocean study, known as the Joint Air-Sea Monsoon Interaction Experiment, or JASMINE, is a joint venture of Colorado University, the University of Washington, the University of Hawaii, the National Oceanic and Atmospheric Administration, the National Science Foundation, NASA and several Australian agencies.

Last summer, researchers used the NOAA ship Ron Brown to make several north-south passes in India's Bay of Bengal totaling about 10,000 miles. The team measured gradient changes in water temperatures and salt content to more than 1,500 feet, used six types of radar, six to eight weather balloons each day and data from European satellites to measure atmospheric temperatures and wind speeds from the sea surface to about 12 miles high.

"I think people have become a bit 'El Niņo-centric,'" said Webster. "Certainly El Niņo plays a major role in climate variation on Earth, but there also is a lot of independent climate variability. If we can better understand the engine driving the Indian Ocean monsoon, we will be better able to forecast its onset and impacts."

The research was published in the Sept. 23 issue of Nature.

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