Tuesday, October 17, 2006

El Niño: He's Back

It was a clear, calm day at the bottom of the Earth when an iceberg known a B15A suddenly broke into a half-a-dozen pieces. Scientists, monitoring the Antarctica ice shelf from satellite photographs, were stunned and confused. What could cause the 60-mile-long iceberg to fall apart?

The answer was even more surprising. Seismometers planted in the ice suggested the iceberg had been moving up and down and from side to side before it broke apart. The scientists figured a storm somewhere might have generated strong waves that destroyed the iceberg.

That “somewhere” turned out to be more than 8,000 miles away.

“Our jaws dropped,” said Douglas MacAyeal of the University of Chicago. “We looked in the Pacific Ocean and there, 8,000 miles away, six days earlier, was the winter season’s first really big, nasty storm that developed and lasted about a day and a half in the Gulf of Alaska.”

Writing in the journal Geophysical Research Letters, MacAyeal said his discovery shows how weather in one region of the world can affect events far away.

Another worldwide weather maker is taking shape in the rapidly warming waters of the equatorial Pacific Ocean. On September 13, the Climate Prediction Center reported that region’s sea surface temperatures were 0.5 degree centigrade above normal. Since then, the water temperature has continued to increase leading scientists to an unmistakable conclusion: El Niño is back.

El Niño is the nickname for the periodic warming of the Pacific Ocean near the equator. For reasons still not clearly understood, every three to five years the ocean waters, from the coast of Peru stretching thousands of miles to the middle of the Pacific Ocean, heat up.

The extra heat and moisture released into the atmosphere produces striking differences in the temperature between the equator and areas to the north. That, in turn, leads to a much stronger jet stream (a river of air five to seven miles above the Earth) and a shift in weather patterns around the world.

In 1982, one of the strongest El Niño’s in history was blamed for some 2,000 deaths and estimated losses totaling $13 billion worldwide. Peru had its worst rainfall in history; 11 feet of rain in locations which usually got six inches. Droughts, dust storms and forest fires swept through Australia, Indonesia and Africa. There was a warm, wet spring in the east coast of the United States; shark attacks off the Oregon coast and a rise in bubonic plague cases in New Mexico.

No one knows the strength of this year’s El Niño but El Nino’s in the past have had a huge impact on Florida’s winter weather.

“During strong El Niño events Florida experiences more frequent and stronger low-pressure systems from late fall through early spring,” said Bart Hagemeyer of the National Weather Service Melbourne office. “This increased storminess brings slightly cooler than normal temperatures, a greater chance of heavy rain and flooding, and severe weather such as tornadoes and damaging wind storms.”

In other words, a dry season that’s not so dry, but not necessarily very cold. While Hagemeyer expects more frequent cold fronts this winter the threat of a freeze is quite low.

“This is because during El Niño conditions warmer than normal temperatures are found over western Canada and the U.S. Northern plains which are the source for cold arctic air outbreaks in Florida,” said Hagemeyer. “During an El Niño season the average jet stream track is further south so it's not pulling down arctic air from the far north to Florida.”

If El Nino sticks around through next summer, that southern jet stream track will play a huge role during the hurricane season. El Nino is the hurricane terminator.

In 1997, part of the current cycle of increased hurricane activity, another El Nino had a huge impact on that year’s hurricane season. Eight named storms formed that summer and fall but only one, Hurricane Erika, developed in the deep tropics and only Hurricane Danny impacted the United States.

The Climate Prediction Center continues to monitor this year’s developing El Nino and will issue an update soon.

Posted at 12:18 PM