Big­gest tor­nado out­breaks are spawn­ing more twis­ters

Kuwait Times - - HEALTH -

WASH­ING­TON: The most ex­treme tor­nado out­breaks are mys­te­ri­ously spawn­ing many more twis­ters than they did decades ago, a new study claimed.

The once-ev­ery-five-years-or-so out­break that might have in­volved 12 tor­na­does 50 years ago now has on av­er­age about 20, said Columbia Univer­sity ap­plied physics pro­fes­sor Michael Tip­pett, lead au­thor of the study in Thurs­day’s jour­nal Sci­ence .

The study comes in the end of a year that has been on track to have the fewest tor­na­does on record, but is also on the heels of the out­break Tues­day night and Wed­nes­day morn­ing that killed five peo­ple and in­jured at least 46 in Alabama and Ten­nessee √¢¬Ä¬î pre­cisely the kind of out­break Tip­pett stud­ied.

As of now, there were 36 tor­nado re­ports Tues­day in Alabama, Ten­nessee, Mis­sis­sippi and Louisiana, half of them were the stronger type Tip­pett stud­ied, said me­te­o­rol­o­gist Pa­trick Marsh of the Na­tional Weather Ser­vice’s Storm Pre­dic­tion Cen­ter in Nor­man, Ok­la­homa.

Tip­pett and col­leagues looked at just the most ex­treme out­breaks and tor­na­does that are above the min­i­mal wind rat­ing and found a steady uptick in the big­gest out­breaks since the mid-1960s. “Some­thing’s up,” Tip­pett said. “The tor­na­does that do oc­cur are oc­cur­ring in clus­ters. It’s not any in­crease in the (to­tal) num­ber of tor­na­does.”

Marsh said un­til Tues­day’s out­break, there had been 830 tor­na­does all year , which was be­low the pre­vi­ous low for that date of 920. The nor­mal num­ber through late Novem­ber is closer to 1,300. While 2011 was one of the busiest tor­nado years for the size of twis­ters that Tip­pett stud­ied, 2012 was one of the qui­etest, he said.

Un­like other spikes of ex­treme weather in re­cent years, Tip­pett and col­leagues could not find the fin­ger­prints of man-made global warm­ing in the change. “It’s not what we ex­pected,” Tip­pett said. “Ei­ther it’s not cli­mate change be­cause not ev­ery­thing is, or it is some as­pect of cli­mate change we don’t un­der­stand yet.”

Eight out­side ex­perts were split about whether the study made sense. “This is re­ally im­por­tant step for­ward in the de­tec­tion in the change of fre­quency of oc­cur­rence of these events,” Stan­ford Univer­sity pro­fes­sor Noah Dif­f­en­baugh said.

But some of the other sci­en­tists said im­proved re­port­ing and ur­ban sprawl in­creases the num­ber of re­cent tor­na­does and negates some of the trend Tip­pett found. They also dis­agree with the par­tic­u­lar type of mea­sure­ments that Tip­pett used and some of his def­i­ni­tions. “It’s a use­ful ex­er­cise,” said Ok­la­homa Univer­sity me­te­o­rol­ogy pro­fes­sor Howard Bluestein, “but I would be very, very care­ful in ac­cept­ing it.”

— AP

ROS­ALIE, Alabama: In this Nov. 30, 2016, photo, Gregg Jef­ferey, left, and his son Tyler help a fam­ily friend clean up their busi­ness at Ros­alie Plaza af­ter a pos­si­ble tor­nado ripped through the town.

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