Photograph: Scientists have found that the Indian Ocean, like the Pacific, has an El Niño. A warm pool in the Indian Ocean moves eastward (1 to 3) in a cycle of 3 to 7 years. The same phenomenon occurs in the Pacific (4 to 6). The research will enable better forecasting of climate changes that cause droughts and floods in the Indo-Pacific region, and in the equatorial Atlantic, where a warm pool (7) develops 12-18 months after the El Niño in the Pacific and Indian Oceans.
Scientists this week reported that the Indian Ocean, like the Pacific Ocean, has an "El Niño"--the cyclical shifts in upper ocean temperature that dramatically affect the world's weather.
The research for the first time links the two vast oceans in a related pattern occurring over 3 to 7 years, whose effects on the world's climate could be more far-reaching than previously thought. The discovery of a more global aspect to the El Niño/Southern Oscillation (ENSO) could advance scientists' understanding of the Pacific El Niño, improving their ability to forecast El Niño-spawned droughts, floods and storms all over the world.
The research was conducted by Yves M. Tourre, a research meteorologist at Columbia's Lamont-Doherty Earth Observatory and professor at Western Connecticut State University, and Warren B. White, a research oceanographer at the Scripps Institution of Oceanography, U.C.-San Diego. The scientists reported the results Dec. 7 at the American Geophysical Union's meeting in San Francisco and they will be published this spring in the Journal of Physical Oceanography.
The scientists analyzed global ocean temperature changes from 1979-91, using more than 650,000 measurements collected over the period by commercial ships, fishing boats, research vessels and naval warships the world over. These high-quality subsurface temperature measurements were compiled by the Integrated Global Ocean Services System (IGOSS), operating under the auspices of the United Nations. For the first time, these data have been made available in real time via satellites, giving scientists a new tool for conducting research and forecasts, they said.
The ships deployed mainly expendable bathythermographs (XBTs) -- probes that fall through the water column to measure water temperatures at numerous depths. The scientists created a data set of temperature changes not only at the sea surface, but over the upper quarter-mile of ocean, where massive amounts of heat are stored and transported around the global ocean. They used this new record of upper ocean temperatures for the first time, and more conventional data on sea surface temperatures, to track ENSO.
ENSO is an irregular cycle, repeating every 3 to 7 years, during which global wind patterns and pools of very warm surface waters are displaced from one side of equatorial oceans to the other side. The pool's displacement is associated with corresponding displacements in rainfall and winds, both locally and globally.
Historically, the warming of surface waters off South America's west coast was called El Niño (the child), since the recurring phenomenon usually coincided with Christmastime. But El Niño is now recognized as a local manifestation of the global ENSO cycle, whose variations have direct climatic impacts and socio-economic consequences over the entire globe, ranging from destructive floods and droughts to disruptions in commercial fisheries and agriculture. Its effects are felt from eastern Australia to Brazil, from North America to Europe and from Africa to India.
Using global records of both surface and subsurface temperatures, Tourre and White analyzed the Pacific, Indian and Atlantic oceans separately. Then they compared the ENSO signals they found in the three oceans, finding links over the global tropical ocean.
They discovered an El Niño pattern in the Indian Ocean that is in lock-step with that in the Pacific Ocean. During the same periods when the Pacific warm pool migrated eastward to create the El Niño in 1982-83 and in 1986-87, El Niño also formed in the Indian Ocean. Tourre and White found that ENSO cycles in the Indian and Pacific oceans may influence each other. On the other hand, dynamic processes within each ocean appear to be different.
In both oceans, the warm pool in the western part moves eastward along the equator. In the Pacific Ocean, it moves to the coast of South America, where the warmest sea surface temperatures form during the El Niñoo. In the Indian Ocean, it moves to the central region, where the warmest sea surface temperatures form during the Indian El Niño. El Niño in both oceans are in phase.
Subsequently, the warm pool in the eastern Pacific dissipates, while the warm pool in the Indian Ocean continues eastward to Indonesia and southward into the Timor Sea north of Australia. The warm pool in the Indian Ocean propagates eastward along the equator more slowly than it does in the Pacific Ocean. Unlike the vaster Pacific Ocean, circulation in the smaller Indian Ocean appears to be strongly influenced by the powerful monsoon winds that blow along coastlines of Africa, India and Indonesia, scientists said. As in the Pacific Ocean, recognition of a cyclical El Niño pattern in the Indian Ocean holds the potential for forecasting rainfall in the Austral-Asia egion six to 12 months in advance.
The National Oceanic and Atmospheric Administration and the NSF supported the research.
