Scott Curtis, who spent six weeks this summer with a team of NASA researchers surveying rain data captured by NASA satellites just before the 2002-03 El Niño, produced an index that uses rainfall conditions in the Indian Ocean to determine when an El Niño might occur.
Curtis said the El Niño Onset Index (EOI) could give scientists and communities an earlier warning to prepare for the effects of El Niño. The team's findings were endorsed this year in an article in the Journal of Geophysical Research — Atmospheres. The index is available to scientists for analyzing possible future El Niño events.
The researchers observed a dramatic shift in the climate of the eastern Indian Ocean in 2001-2002, as westerly winds increased and the weather flip-flopped from dry to wet. Turning to National Aeronautics and Space Administration satellites for answers, researchers tracked two cases where wind, rainfall, and warmer sea surface temperatures moved from the Indian to the Pacific Ocean in early 2002 before the 2002-03 El Niño.
"This study expands on recent work linking rain and wind changes over the last 25 years to the development of El Niños," Curtis said.
The researchers developed the El Niño Onset Index using only rainfall data, after modeled wind data revealed no significant shift, Curtis said. "Because the rainfall data has been a consistent indicator of an oncoming El Niño, as compared to the wind data, only the rainfall data was used to construct the EOI."
Named after the Christ child by Peruvian fishermen who noticed the warmer waters around Christmastime, El Niño happens every two to seven years when a warming of the ocean surface off the western coast of South America occurs and cold, nutrient-rich water fails to surface from the ocean bottom. El Niño affects Pacific jet stream winds, altering storm tracks and creating unusual weather patterns in various parts of the world.
The National Oceanic and Atmospheric Administration said a weak El Niño, which the EOI did not predict, is under way. Curtis explained that the EOI might not be sensitive enough to register weak episodes. After computing the EOI back to 1979, the only El Niño that was not "predicted" was the weakest event in 1993.
For this work Curtis used NASA's Tropical Rainfall Measuring Mission (TRMM) and QuikScat satellite data and collaborated with Robert Adler, George Huffman and Guojun Gu, all of NASA's Goddard Space Flight Center in Greenbelt, Md. In 2003, Curtis received a $279,000 from NASA grant to conduct the research. The results further the team's research published in Geophysical Research Letters in 2002.
ECU News Bureau