Thursday, July 2, 2009

New Type Of El Nino Could Mean More Hurricanes Make Landfall

UPDATE below.
Amazing stuff. We'll come back to this in mid-August to see how ENSO 3; 4 and 3.4 are developing.
From ScienceDaily:
El Niño years typically result in fewer hurricanes forming in the Atlantic Ocean. But a new study suggests that the form of El Niño may be changing potentially causing not only a greater number of hurricanes than in average years, but also a greater chance of hurricanes making landfall, according to climatologists at the Georgia Institute of Technology. The study appears in the July 3, 2009, edition of the journal Science.

"Normally, El Niño results in diminished hurricanes in the Atlantic, but this new type is resulting in a greater number of hurricanes with greater frequency and more potential to make landfall," said Peter Webster, professor at Georgia Tech's School of Earth and Atmospheric Sciences.

That's because this new type of El Niño, known as El Niño Modoki (from the Japanese meaning "similar, but different"), forms in the Central Pacific, rather than the Eastern Pacific as the typical El Niño event does. Warming in the Central Pacific is associated with a higher storm frequency and a greater potential for making landfall along the Gulf coast and the coast of Central America.

Even though the oceanic circulation pattern of warm water known as El Niño forms in the Pacific, it affects the circulation patterns across the globe, changing the number of hurricanes in the Atlantic. This regular type of El Niño (from the Spanish meaning "little boy" or "Christ child") is more difficult to forecast, with predictions of the December circulation pattern not coming until May. At first glance, that may seem like plenty of time. However, the summer before El Niño occurs, the storm patterns change, meaning that predictions of El Niño come only one month before the start of hurricane season in June. But El Niño Modoki follows a different prediction pattern.

"This new type of El Niño is more predictable," said Webster. "We're not sure why, but this could mean that we get greater warning of hurricanes, probably by a number of months."

As to why the form of El Niño is changing to El Niño Modoki, that's not entirely clear yet, said Webster.

"This could be part of a natural oscillation of El Niño," he said. "Or it could be El Niño's response to a warming atmosphere. There are hints that the trade winds of the Pacific have become weaker with time and this may lead to the warming occurring further to the west. We need more data before we know for sure."

In the study, Webster, along with Earth and Atmospheric Sciences Chair Judy Curry and research scientist Hye-Mi Kim used satellite data along with historical tropical storm records and climate models.

The research team is currently looking at La Niña, the cooling of the surface waters in the Eastern and Central Pacific.

"In the past, La Nina has been associated with a greater than average number of North Atlantic hurricanes and La Nina seems to be changing its structure as well," said Webster. "We're vitally interested in understanding why El Niño-La Niña has changed. To determine this we need to run a series of numerical experiments with climate models."

UPDATE: We don't usually copy out the entire body of a story. The thinking is, a source deserves the traffic, should a reader be interested enough to click the link. In this case the SD piece appears to be the press release and we linked and named the source in the intro.

On the other hand, we have this version, mailed by a reader, which has more original content. From Science News:

New cyclone predictor

Occasional sea-surface warming in central Pacific linked with more, stronger hurricanes in North Atlantic
Warmer-than-normal sea-surface temperatures in the central Pacific lead to stronger, more frequent tropical storms and hurricanes in the North Atlantic, a new analysis suggests. Unlike the more familiar El Niño, or warming in the equatorial region of the eastern and central Pacific, trends in central Pacific warming alone are more predictable and may offer forecasters a more accurate method of anticipating hurricane activity during the upcoming year, scientists say.

The sea-surface warming characteristic of El Niño typically stretches along the equator from the coast of South America to the international date line, with the largest temperature anomalies in the eastern Pacific. During El Niño episodes, the number of tropical storms and hurricanes — both called cyclones — is lower than average across the North Atlantic, says Peter J. Webster, an atmospheric scientist at Georgia Tech in Atlanta. But when the equatorial sea-surface warming is concentrated only around the international date line, hurricane activity is much higher than normal, Webster and his colleagues report in the July 3 Science.

“This is a pattern that we [scientists] hadn’t really recognized before,” comments Chris Landsea, an atmospheric scientist at NOAA’s hurricane research division in Miami. He says the finding is “an advance in the field.”

Webster and his colleagues analyzed patterns in North Atlantic cyclone activity from 1950 through 2006 during August, September and October, the height of hurricane season. As many previous studies had noted, the number and strength of tropical cyclones were markedly lower in El Niño years than during La Niña episodes, when sea-surface temperatures in the eastern and central Pacific are substantially cooler than normal. Unlike previous research, says Webster, the new study reveals that when sea-surface warming is confined to the central Pacific, hurricane activity is higher, particularly in the Caribbean, the Gulf of Mexico and along the eastern coast of the United States....MORE