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One of the biggest, meanest El Niño episodes of the 20th Century came and went and almost nobody noticed. It was 1918, a year when many people had their hands full just staying alive. The first World War was ravaging Europe, and an influenza pandemic of Biblical proportions was killing more than 50 million around the world.

Nearly a century later, a new dataset reveals the magnitude of unusually warm water temperatures on the surface of the ocean along the equator in the middle of the Pacific. Beyond the reach of coastal observations, in shipping lanes vacated by the strategic demands of a North Atlantic war, a powerful El Niño was hiding out in plain sight, bending the weather to its whims.

What people did notice, of course, was what El Niño did to the weather, including dramatically warmer winter temperatures in the eastern United States — but especially the failure of the summer monsoon in India, which brought on drought and famine, weakening a vulnerable population at the worst possible time.  As many as 16 million people may have perished in India from the virus known as "Spanish Flu."

Completion of a complex, computer-intensive project of "reanalysis" which fills in the missing weather data for the first half of the 20th Century has just now made possible what oceanographer Benjamin S. Giese at Texas A&M University describes as "the first comprehensive description of the structure and evolution of the 1918/1919 El Niño."  The image above is an ocean model simulation produced by Giese's team.

Meteorologists have taken information contained in old hand-drawn weather maps and created three-dimensional maps of the atmosphere that depict weather conditions every six hours from the surface to 36,000 feet aloft, the level of the jet stream.  For a study available online and about to be published in the Bulletin of the American Meteorological Society, Giese and colleagues recreated the 1918-'19 El Niño by configuring an ocean model with this "reanalyzed" atmospheric data.

Other researchers have used the output of this reanalysis project, performed by scientists at the University of Colorado and the National Oceanic and Atmospheric Administration, to resolve other climate and weather mysteries. 

One recent study of the "Dust Bowl," for instance, established that the wrenching 1930s drought was the result of unusually cool Pacific sea surface temperatures.  (This photo, courtesy of NOAA, shows a dust storm overtaking Stratford, TX in 1935.)  Another serious drought 20 years later in the upper Midwest, in contrast, was seen as the consequence of natural atmospheric variability.  Researchers also used the reanalysis data to recreate the meteorological conditions that provoked the so-called "Knickerbocker Storm" that dumped heavy snow over the East Coast in 1922.  In Washington, D.C., the roof of the Knickerbocker Theater collapsed from the weight, killing 98 people.

A more accurate and detailed record of 20th Century meteorology holds promise for better understanding of future conditions as well as past events. Using the new dataset, researchers hope to develop more detailed pictures of the regional consequences of on-going global changes, for example, bridging the gap between climate and weather.