|
|
"Tornado Intercept" Offers Rare Peek at a Twister Touchdown |
|
Stefan Lovgren for National Geographic News |
| December 16, 2005 |
|
On TV: Watch Intercept premiering Sunday, December 18 at 8 p.m. ET/PT on the National Geographic Channel. Documentary filmmaker Sean Casey recently teamed up with meteorologist Josh Wurman to push twister science further than ever before. With Casey driving his steel-plated tornado intercept vehicle into a raging twister, Wurman and his caravan of Doppler trucks followed close by to collect data from the tornado's most destructive—and least understood—zone: the lower 30 feet (9 meters). National Geographic News spoke with Wurman on the phone from Boulder, Colorado, where he directs the Center for Severe Weather Research. He receives funding for his research from the National Science Foundation and the National Geographic Society. I'm sure you've been asked this many times, but … are you nuts? We're doing a very carefully choreographed deployment around the tornado, using mobile radar that can scan through tornadoes every few seconds. We know exactly where the tornado is, how big it is, how strong it is, how fast it's moving. We have quantitative information about many parameters in the tornado and can do things safely that may appear to be on the edge if you didn't have that kind of information. What kind of information about the tornadoes do you get from the radar? We have intercepted over a hundred tornadoes with radar. Our goal is to get as complete a picture of the tornado as we can. The radar enables us to take multiple slices through the tornado every ten seconds to a minute, and make 3-D images of the outside and the inside of the tornado. In addition, what we want to do is measure the thermodynamic properties around the tornado. It turns out that a lot of the physics that's driving why the tornado has certain wind speeds, why it's large, or why it's getting stronger is driven by the thermodynamics in the air. What's the range of the radar? How close to the tornado you have to get? The [radar] can see out a hundred miles or more. But we need to get much closer—usually anywhere from half a mile to three miles [one to five kilometers] away—where you get much finer detail. The limitation is that we can't see very close to the ground. Inevitably there are small hills, trees, bushes, and fences in the way. This means we're not very effective with the radar below 50 feet [15 meters]. And that's where the tornado intercept vehicle, or TIV, comes in? Describe it for us. It's a Ford truck with its body taken off. It's been armored with 8,000 pounds [3,630 kilograms] of steel plating. It's very difficult to lift because it's low to the ground. It's aesthetically ugly, but functionally it's beautiful. What it lets us do is extend observations into the tornado by driving the truck into [the twister]. And you get information that you otherwise wouldn't be able to get? We can measure what's actually happening on the ground or very close to the ground in a tornado. That's a critical region for us to understand, both from a scientific point of view and from an engineering point of view. [For example], there are different numbers flying around for how fast tornado wind speeds are. I've measured with the radar winds up to 300 miles an hour [483 kilometers an hour], but wind engineers with computer simulations and lab experiments know that you could produce the worst possible damage that has ever been observed with winds that are only about 200 miles per hour [322 kilometers an hour]. What's happening is that the winds are a little bit less at the ground level than they are at 50 or 100 feet [15 or 30 meters]. You used the TIV to collect data on a tornado this year. Tell me about that. It was a moderately strong tornado … that went over open country near Jayton, Texas. The TIV basically drove right up there, but the tornado didn't cooperate and kind of dodged around the road. The center missed the TIV by about a hundred meters. They were at the edge of the tornado's flow. It was really groundbreaking for us, because we were able to measure wind speeds about 50 feet [15 meters] over the TIV and at 10 feet [3 meters] above the ground. How confident are you that this vehicle can withstand the power of a tornado? The key is to do this with the radar. What we provide the TIV is critical safety information. We can tell them every ten seconds how strong those winds are. Are they getting stronger or are they getting weaker? How close to the center of the tornado can you go? We're able to say, That tornado has 120-meter-a-second [268-mile-an-hour] winds, it's scouring everything in its past, and you really don't want to go to the heart of it because it can hurt you. No rational explorer takes undue risks. Successful scientific exploration involves living to repeat and confirm discoveries. How could this information help engineers to build more storm-resistant buildings, for example. There are basic questions that we don't know the answers to right now. For example, What's worse: a 300-mile-an-hour [483-kilometer-an-hour] wind for a second or a 200-mile-an-hour [322-kilometer-an-hour] wind for a minute? You could engineer different kinds of structures to withstand those different kinds of things. What about forecasting tornadoes? There are thousands of severe, rotating super-cellular thunderstorms every year. Probably only a quarter of them produce tornadoes, and we don't have a good ability to distinguish which ones will and which ones won't. The other thing we need to be able to do in areas where tornadoes do occur is to warn earlier and provide tornado intensity forecasts. This is important because if I knew an F0 tornado was coming, I might just get into the bathtub. [Scientists rate tornado intensity after the fact using the Fujita Scale, a scale of zero through five that measures how much damage a storm does when it hits a man-made structure.] But if I'm told with half an hour's warning that an F5 is coming, I might take the risky action of getting into my car and hoping my car isn't going to get stuck in the tornado, because I know my bathroom is not going to survive an F5. Free E-Mail News Updates Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample). |
| © 1996-2008 National Geographic Society. All rights reserved. |