Friday, May 27, 2011

A Great Q&A About Tornadoes

The Facts (and Fiction) of Tornadoes
Q: How bad has this year’s tornado season been, relative to other years?
A: Extraordinarily bad, even by historical standards. The death toll, now at more than 480, is the highest since 1953, when an outbreak of twisters across the Midwest and the Northeast claimed 519 lives. The high death toll this year is all the more remarkable considering that early warning systems are in place throughout tornado country, made possible by the advent of Doppler radar. Many tornado experts believed that the advances in technology had greatly diminished the risk of mass tornado fatalities.
“We never thought there’d be another year of deaths like this, with all our warning systems,” said Thomas P. Grazulis, a tornado historian.
Since 1875, there have been just 15 years with more than 360 tornado deaths, and none since 1975. The single deadliest tornado year in the United States was 1925, with 794 fatalities. This year now ranks eighth on the list of deadliest tornado years.
The tornado that struck Joplin, Mo., on Sunday, with its death toll now standing at 122, is the deadliest in recorded history. The second deadliest was a twister that barreled through Flint, Mich., in 1953, killing 116.  JOHN COLLINS RUDOLF
Q: How long does it take for a town to recover from a tornado, in comparison with a hurricane or other type of natural disaster?
A: As destructive as tornadoes can be, the damage they cause tends to be confined to a swath within a town or in the countryside, while hurricanes, floods and earthquakes can affect a wide region. The water and shifting soils that accompany such events often cause additional disruption.
Experts say there is no simple timetable for recovery. But in general, the recovery from a tornado is quicker than from more multifaceted disasters.
“With something that is more localized, in effect, it’s easier to get resources up to the problem,” said Joseph Booth, executive director of the Stephenson Disaster Management Institute at Louisiana State University.
Mr. Booth noted that after Hurricane Katrina hit, “in the core damage area and for 50 miles past, you had no electricity or a large amount of structures that were even capable of sustaining the force that was being sent in to deal with it.” The hurricane also destroyed emergency vehicles and equipment, hampering police officers, firefighters and paramedics. So while the images and reports from tornadoes in Missouri, Minnesota and Alabama are “absolutely horrific,” Mr. Booth said, “it’s easier to deal with a big problem than it is to deal with an enormous problem.”
Robert Kates, a co-author of “Reconstruction Following Disaster,” said natural disasters had an arc of recovery that fell into recognizable patterns.
“There’s the emergency, in which you’re doing search and rescue and you’re housing people in evacuated spots” and just trying to get by, Mr. Kates said. “The second phase is where you repair everything that’s repairable,” from patching streets to restoring water and gas lines. The third stage is reconstruction.
In general, he said, the restoration takes 10 times as long as the emergency phase and reconstruction takes 10 times as long as restoration. The six weeks of paralysis after Hurricane Katrina, for example, can be expected to translate into 11 years until full recovery. Mr. Kates said that he had never applied the disaster-recovery template to tornado damage, in part because the destruction was so localized, but that the same principles should apply.  JOHN SCHWARTZ
Q: Can the intensity of this year’s tornadoes be blamed on climate change?
A: Probably not. Over all, the number of violent tornadoes has been declining in the United States, even as temperatures have increased, making it likely that this year’s twister outbreak is simply a remarkable and terrifying  but natural  event.
Climate science has long predicted that global warming will cause more weather extremes, however, and statistics suggest that this has started to happen. In most areas of the world where good weather data is available, instances of heavy precipitation are rising, often leading to flash flooding. And the same thing is true of heat waves; in the United States, new high-temperature records for a given date now occur twice as often as record lows.
That said, scientists are reluctant to attribute any specific weather event to global warming. And, at least so far, only a handful of studies have suggested that tornadoes are likely to become more frequent or more intense on a warming planet. Frustratingly, it is likely to be a year or two before we get good published analyses of the causes for this season’s strange weather  and it may be decades before science can conclusively demonstrate whether or not human-driven warming is affecting tornado frequency.  JOHN COLLINS RUDOLF and JUSTIN GILLIS
Q: How do tornadoes get their shape?
A: Tornadoes form in several ways, but in the Midwest and the South in particular, they usually form in unstable conditions, where warm moist air at the surface meets a line of dryer, cooler air higher up. The basic spinning shape initially is a result of wind shear  wind at different speeds and from different directions in the unstable air creates a horizontal rolling tube of air near the surface. The warmer air causes updrafts that can lift this tube up toward the vertical, which causes a larger mass of unstable air to spin. Meteorologists call this rotating upward-moving mass a mesocyclone, and thunderstorms that contain them are known as supercells. Tornadoes are spinning offshoots of these supercells that reach the ground, and while researchers are not exactly sure why they form, it is believed that downdrafts in the thunderstorms may play a role. Under the right conditions, a tornado can suck in so much air, water droplets, dirt and debris that it becomes very large, a mile wide or more. The informal term for these large twisters is “wedge” tornadoes.  HENRY FOUNTAIN
Q: Why does the sky sometimes look green when a tornado strikes?
A: A severe thunderstorm contains large amounts of water  either rain or hail  and water tends to scatter reddish light. When a thunderstorm arrives in late afternoon, light traveling on a straight line from the sun is first depleted of blue wavelengths as it passes through the atmosphere and then of red wavelengths as it passes through the thunderstorm. That leaves the middle part of the spectrum  green or at least greenish. “It’s not far off gray, but it is green,” said William Beasley, a professor of meteorology at the University of Oklahoma.  KENNETH CHANG
Q: How far can an object picked up by a tornado travel?
A: Tornadoes have tipped over trains and sucked up cows, but the objects that travel farthest are, not surprisingly, small and light.
In 1995, researchers at the University of Oklahoma wanted to study the pattern of debris carried long distances by tornadoes. So after a tornado, they asked people to send them identifiable objects, for example, canceled checks, which helpfully include the name and address of the check writer, making it easy to figure out how far the check has traveled.
In five years, more than 1,000 objects were collected, said John T. Snow, dean of the university’s College of Atmospheric and Geographic Sciences, who led the tornado debris project. Among the odder ones was a man’s bowling jacket. “It had his name stenciled on the back of it and the name of the bowling alley,” Dr. Snow said.
Most of the objects landed fairly close, 15 to 20 miles from where they started. A few traveled more than 60 miles. The farthest an object traveled was more than 150 miles.  KENNETH CHANG
Q: How well can meteorologists predict the path of a tornado?
A: John Ferree, a researcher with the National Severe Storms Laboratory in Norman, Okla., said forecasters typically issued a warning for about three of every four tornadoes, and rarely missed a strong tornado like the one that hit Joplin. But predicting the precise touchdown point and path is difficult. Meteorologists can see from radar where the center of the wind circulation is, but that is a mile up in the air, and the path to the ground may be slanted. Normally, forecasters can place a tornado within about five miles of its touchdown point, Mr. Ferree said.
Forecasters can also predict the compass direction of the tornado within 20 degrees to 30 degrees. Large tornadoes that develop from the rotating thunderstorms called supercells can sometimes slow down and then veer to the right as air circulates around them, Mr. Ferree said, adding, “Those are ones you have to watch out for.”  HENRY FOUNTAIN
Q: What is the risk of being killed by a tornado in the United States?
A: Nationwide, the risk is 1 in 5 million, according to Dr. Harold E. Brooks, a research meteorologist at the National Severe Storms Laboratory, part of the National Oceanic and Atmospheric Administration.
Before 1925, the death rate was nine times as high. After tornadoes that year killed 695 people in Missouri, Illinois and Indiana, mass communication improved, public awareness increased and builders began making stronger houses. As a result, Dr. Brooks said, tornado deaths declined for decades. But the decline slowed in the 1990s because more and more people began living in mobile homes, which are tossed about by the high winds. People who live in trailers or mobile homes are 15 times as likely as those in permanent housing to be killed by tornadoes. Dr. Brooks said that this year, the rate of tornado deaths among mobile-home residents might reach 50 per 5 million.
Although the risk would seem to be higher in the “Tornado Alley” region of the South and the Midwest, it is not possible to calculate reliable figures by state or region, Dr. Brooks said, because the numbers are too small to be statistically meaningful.  DENISE GRADY
Q: After Hurricane Katrina, there were hundreds of homeless dogs and cats. What has happened to people’s pets in Joplin?
A: About 70 animals  dogs, cats and some parakeets and cockatiels  have been taken to the Animal Adoption and Resource Center in Joplin so far, said Lisa Buehler, the manager there. But the shelter is expecting many more to arrive in coming days.
“We really don’t know yet the full extent of it,” Ms. Buehler said. “They’re still searching for people, so it’s going to take a while to catch up.”
She said that the shelter had veterinarians standing by to tend to wounded animals and that several injured dogs had already arrived. The center’s building is “pretty sturdy,” Ms. Buehler said, but if a tornado were to threaten the shelter, “we have so many animals in the building it would be physically impossible to move them to another building.”  ERICA GOODE
Q: Could lives and property have been saved if residents in the areas struck by tornadoes had opened a window or two in their houses? And should drivers have stayed in their cars or sought safety under highway overpasses?
A: The idea that opening windows can spare a building from damage from tornadoes is a common misconception. By equalizing air pressure with the low-pressure tornado outside, the thinking goes, the building will not explode from within as a result of the pressure difference. But experts say that opening windows is useless; internal forces do not damage houses  powerful winds and, most especially, the debris that those winds throw around like missiles, damage and destroy houses from outside.
While there has been some debate about whether it is safe to remain in a car  one study in 2002 suggested it might at least be safer than remaining in a mobile home  most experts say that it is practically impossible to outrun a tornado and that remaining in a car is dangerous. It is best to get out and seek shelter  in the basement of a building, if possible, or in a ditch or other low-lying area away from trees. Experts say that the idea that huddling under a highway overpass will provide a measure of safety is also false. The high winds can just as easily blow under the overpass as over it.  HENRY FOUNTAIN

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