US tornado stronger than Hiroshima bomb
Seth Borenstein, AAP May 22, 2013, 7:59 am
David Wheeler spent an agonizing three hours looking for his son Gabriel, who was one of the last rescued from the rubble of Briarwood Elementary after a massive tornado blew through. (May 21)
The massive killer tornado in Oklahoma was caused by a precise combination of wind, humidity and rainfall, experts say.
The awesome amount of energy released on Oklahoma City and its suburbs dwarfed the power of the atomic bomb that levelled Hiroshima.
On Tuesday afternoon, the National Weather Service in the US gave the tornado the top-of-the-scale rating of EF-5 for wind speed and breadth and severity of damage. Wind speeds were estimated at between 320km/h and 337km/h.
Several meteorologists contacted by The Associated Press used real-time measurements to calculate the energy released during the storm's life span of almost an hour.
Their estimates ranged from eight times to more than 600 times the power of the Hiroshima bomb.
The tornado at some points was two kilometres wide and its path stretched for 27 kilometres and 40 minutes.
That's long for a regular tornado but not too unusual for such a violent one, said research meteorologist Harold Brooks at the National Severe Storms Laboratory.
Less than one per cent of all US tornadoes are this violent - only about 10 a year, he said.
It was the third strong storm to hit the suburb of Moore in 14 years and some people are wondering why.
It's a combination of geography, meteorology and lots of bad luck, experts say.
If you look at the climate history of tornadoes in May, you will see they cluster in a spot - maybe 160 kilometres wide - in central Oklahoma, said Adam Houston, meteorology professor at the University of Nebraska, Lincoln.
That's the spot where the weather conditions of warm, moist air and strong wind shear needed for tornadoes combine in just the right balance.
Several meteorologists also believe "bad luck" is the reason the suburb of Moore has been hit repeatedly by violent tornadoes.
Scientists know the key ingredients that combine in a devastating tornado. But they are struggling to figure out why they develop in some big storms and not others.
They also are still trying to determine what effects, if any, global warming has on tornadoes.
