TOPEX/Poseidon Team/CNES/NASA (APOD)

Trouble brewing. Trouble brewing. Satellite observations show telltale signs of an El Niño returning (red and dark-blue zones).

Problem Child El Niño Has Returned

Batten down the hatches! The disruptive weather pattern known as El Niño has developed once again in the central Pacific Ocean, the first time since 2006, scientists announced today. Satellite instruments have recorded a band of telltale warming in surface waters of about 1°C. That could mean damaging storms this winter in California and across the southern half of the United States, as well as heavy rains in Central and South America, drought in Southeast Asia and Australia, and less productive fisheries in the eastern Pacific. On the positive side, El Niño's return also tends to moderate the Atlantic hurricane season and bring milder winters to North America.

For more than a century, ship captains and fishers have been aware of a recurring pattern in the weather in the eastern Pacific, which tends to repeat itself every 3 to 4 years. The pattern is known as El Niño--or "The Boy Child"--because its effects seem to be felt the most around Christmastime. Scientists now understand that an El Niño period begins when a narrow but well-defined band of surface water, at least 0.5°C warmer than normal, accumulates in the eastern equatorial Pacific and spreads westward during late spring and early summer (see diagram). Satellite data have now confirmed just such a pattern, report scientists at the U.S. National Oceanic and Atmospheric Administration (NOAA).

What isn't yet known is how strong an El Niño will eventually develop and how long it is likely to last. That's because the data collected so far are insufficient to determine those factors. But NOAA's Climate Prediction Center in Camp Springs, Maryland, estimates that for the next several months the overall effect across the United States should be mild. Whether El Niño will stick around for longer and bring destruction remains undetermined.

The previous El Niño, which occurred in 2006–2007, produced relatively tepid effects. But one of its recent predecessors, in 1997–1998, was considered the strongest ever recorded. It caused the average sea-surface temperature in the central Pacific to rise as much as 5°C above normal and warmed average global air temperatures temporarily by about 2.5°C --some five times higher than an El Niño normally generates. That episode also more than doubled 1997–1998 seasonal rainfall over Southern California, washing out roads and bridges and causing landslides.

Posted in Earth