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miércoles, 3 de junio de 2009

Air France Crash Site in Breeding Zone for Storms?

With South America at center, a satellite image captures cloud patterns in the Western Hemisphere on the evening of May 31, 2009.

That same day Air France Flight 447 disappeared, probably off the easternmost coast of South America. The likely crash site is within the intertropical convergence zone, a belt of cloudy, rapidly changing weather that circles the globe near the Equator.

Searchers scouring the Atlantic Ocean for evidence of an Air France crash have spotted debris off northern Brazil's coast (map) possibly belonging to the doomed Flight 447.

The cause of Air France Flight 447's disappearance on Sunday is still unknown, but experts speculate the plane may have encountered turbulence and thunderstorms as it flew from Rio de Janeiro to Paris.

The plane's flight path took it through a tough-to-navigate breeding zone for thunderstorms near the Equator known as the intertropical convergence zone, or ITCZ.

Air France Crash Caused by Tall, Dynamic Storm Clouds?

Northern and southern trade winds crash into each other in the globe-encircling ITCZ. By pushing warm, buoyant equatorial air upward, the convergence helps fuel the zone's almost unceasing series of thousands of small storms.

"You have one thunderstorm building and another dying. It's a constant evolution of things happening," said Larry Cornman, an atmospheric scientist at the National Center for Atmospheric Research in Colorado.

Modern jets typically outmaneuver storms, often flying above thunderclouds.

But the storm clouds in the ITCZ can merge to create towering thunderclouds whose upper reaches are higher than most commercial planes fly.

And because the storm clouds cover an area of hundreds of square miles, it's often not practical for pilots to fly around the storms.

"So what they do is typically try to weave their way through without getting into a thunderstorm," Cornman said.

High Tech Little Help to Air France Flight 447?

Making matters worse, radar is of limited use in the ITCZ.

Air turbulence and strong winds often don't show up strongly, even in areas of pervasive radar coverage, and the ITCZ is not one of those areas.

"You don't have radar [towers] out there on the ground, and there aren't enough aircraft flying through there to get meteorological reports," Cornman said.

Another potential tool, satellite imagery, doesn't have sharp enough resolution or quick enough updates for pilots to make snap decisions, he added.

In such situations, pilots often rely on one another for real-time weather reports, explained Thomas Anthony, director of the Aviation Safety and Security Program at the University of Southern California.

"Pilot reports, or 'pireps,' tells other pilots what's going on. That's where you get your reports about whether turbulence is moderate, light, or severe," Anthony said.

But the ITCZ limits the value of pireps as well, Cornman said.

"The thunderstorms are very dynamic. Even if someone flew through there ten minutes earlier, if you fly even 20 miles [30 kilometers] to the side of where they were, the conditions could be totally different," he said.

While the ITZC can be treacherous for pilots, thunderstorms alone were probably not enough to cause Air France Flight 447 to crash, experts say.

"Almost never is an aircraft accident due to a single failure," Anthony said.

"The thunderstorm may have presented the most immediate cause, but we will find there were contributing factors that led up to it and allowed this to occur."

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