The results may help scientists improve rainfall forecasts around the globe during the life of an El Nino, and they may also offer new insights into how an El Nino develops.

The findings are highlighted in a paper by Scott Curtis of the University of Maryland - Baltimore County and Robert F. Adler of NASA's Goddard Space Flight Center in Greenbelt, Maryland. It appears in the Journal of Geophysical Research - Atmospheres, published by the American Geophysical Union.

In an effort to predict and understand the effects of El Nino, most scientists have focused on seasonal changes in rainfall patterns, like where and when rain falls during winter.

Curtis and Adler take a different approach, looking first at the evolution of rainfall over the Pacific Ocean, which has the power to change the global winds and redirect rainfall patterns around the world.

They found a significant pattern of alternating rainfall for El Ninos since 1979, with wetness in eastern China, dryness over Indonesia, and wetness in the south Indian Ocean and Australia.

They noted that this pattern swings eastward as El Nino weakens.

As it does, rainfall patterns alternate from one area to another. In the eastern Pacific, there is wetness on the Equator, dryness off the coast of Mexico, and wetness off the coast of California. The traditional view of El Nino based on seasonal rainfall patterns obscures these relationships.

El Nino events, like individual thunderstorms, differ in intensity, lifespan, rainfall, and other characteristics, making them difficult to quantify. So, Curtis and Adler set parameters to define El Ninos, based on rainfall that occurs in the equatorial Pacific.

They looked at the periods before rainfall began, when El Nino started, peaked, and faded, and after it ended. They also identified areas around the globe that were consistently wet or dry during each stage of El Nino.

The researchers utilized global rainfall datasets developed from satellites and from rain gauges all over the world, which are part of the Global Precipitation Climatology Project under the Global Energy and Water Cycle Experiment (GEWEX), a project heavily supported by NASA.

Data from the Tropical Rainfall Measuring Mission (TRMM) satellite, which were used in this study, will also help ensure the accuracy of satellites used by the National Oceanic and Atmospheric Administration (NOAA) and Department of Defense.

TRMM is a joint NASA/Japanese Space Agency mission to study tropical rainfall and its implications for climate. Each day, TRMM observes the Earth's equatorial and tropical regions.

In the future, this kind of study may help pinpoint where an El Nino will generate floods, droughts, and changes in rainfall around the globe.

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