Документальный фильм "Wild Weather - What's to Blame?"



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Wild Weather - What's to Blame?

ScienceCasts: Wild Weather

Wild Weather - What's to Blame?

Presented by Science at NASA.

Record snowfall, killer tornadoes, devastating floods: There's no doubt about it. Since December 2010, the weather in the USA has been positively wild. But why?

Some recent news reports have attributed the phenomenon to an extreme "La Nina," a band of cold water stretching across the Pacific Ocean with global repercussions for climate and weather.

But NASA climatologist Bill Patzert names a different suspect: "La Nada." "La Nina was strong in December," he says. "But back in January it pulled a disappearing act and left us with nothing - La Nada - to constrain the jet stream.

Like an unruly teenager, the jet stream took advantage of its newfound freedom, and the results were even more disastrous."

La Nina and El Nino are opposite extremes of a great Pacific oscillation. Every 2 to 7 years, surface waters across the equatorial Pacific warm up (El Nino) and then they cool down again (La Nina).

Each condition has its own distinct effects on weather. The winter of 2010 began with La Nina conditions taking hold.

A "normal" La Nina would have pushed the jet stream northward, pushing cold arctic air, one of the ingredients of severe weather, away from the lower US.

But this La Nina petered out quickly, and no El Nino rose up to replace it. The jet stream was free to misbehave. "By mid-February 2011 the jet stream was meandering wildly around the U.S. The weather pattern became dominated by strong outbreaks of frigid polar air, producing blizzards across the West, Upper Midwest, and northeast U.S." The situation lingered into spring - and things got ugly.

Russell Schneider, Director of the NOAA-NWS Storm Prediction Center, explains: "First, very strong winds out of the south carrying warm, moist air from the Gulf of Mexico met cold jet stream winds racing in from the west. Stacking these two air masses on top of each other created the degree of instability that fuels intense thunderstorms."

Extreme contrasts in wind speeds and directions of the upper and lower atmosphere transformed ordinary thunderstorms into long-lived rotating supercells capable of producing violent tornadoes.

In Patzert's words, "The jet stream, on steroids, acted as an atmospheric mix master, causing tornadoes to explode across the deep south and Tornado Alley, and even into Massachusetts."

The action's not over. This is weather, after all. What will happen next? Please don't say "La Nada."

For more information about wild weather, on Earth and other planets, please visit Science.nasa.gov

Uploaded by ScienceAtNASA on Jun 30, 2011

Visit http://science.nasa.gov/science-news/science-at-nasa/2011/24jun_wildweather/ for the full story.

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Документальный фильм "Wild Weather - What's to Blame?"

















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