August 1, 2008 Meteorologists recently studied the effect of gravity waves on tornado formation. They found that when gravity waves push down on rotating thunderstorms the storm compresses and spins faster. Being able to recognize and track gravity waves before they reach thunderclouds allows meteorologists to better predict tornadoes, increasing both the accuracy of their predictions and the amount of warning time that they can provide.
It has been a devastating and deadly year for tornadoes in the United States. With more than 100 confirmed fatalities, 2008 is said to be the deadliest year for tornadoes since 1998. Now, science may be riding the wave of a new tornado forecasting tool that could help save lives.
In northern Alabama, the're as much a part of the weather as the summer heat. "Tornadoes are a part of life here, just like hurricanes are up in the East. You just expect them," says Mary Ann Campbell, a tornado survivor. In 1989, a powerful Alabama tornado killed 21 people. A tragedy many will never forget. There were many people hurt because it just came so unexpectedly, just right there it came and nobody really had any forewarning, Campbell said.
University of Alabama, Huntsville meteorologists Tim Coleman, Ph.D., and Kevin Knupp, Ph.D., are getting new insight into how some tornadoes form. Their research focuses on these bands called gravity waves -- formed by a sudden disturbance in the atmosphere, such as a change in the wind direction or a thunderstorm's updraft. The waves create ripples in the atmosphere like ripples around a rock thrown into a pond.
When a gravity wave pushes down on a rotating thunderstorm, it makes the storm smaller and spin faster. Just like an ice skater spins faster as she pulls her arms closer to her body.
Dr. Coleman has created computer models, and is studying storms on radar to see how gravity waves can intensify storm rotation. If we can track these waves before they trigger tornadoes, researchers say the benefits could be huge.
"We think it's going to double the lead time on tornado warnings, and increase the accuracy," says Dr. Knupp.
And with powerful storms like this, every second counts.
ABOUT TORNADOES: A tornado begins with a thunderstorm cloud, which can build up a lot of energy. If this energy creates a particularly strong updraft of air, it will form a vortex, much like how a whirlpool forms in a draining bathtub. The air is pulled toward the center in a spiral, forming a tornado under the thundercloud. Wind speeds can reach 200 to 300 mph, and if the dangling vortex touches ground, the combination of the whirling wind's speed, the updraft, and pressure differences can cause severe damage. The path of a tornado is determined by the path of the parent thundercloud, but it will often appear to hop (called a "jumper"). This occurs when the vortex is disturbed, causing it to collapse momentarily and reform.
GRAVITY WAVES: Atmospheric gravity waves are similar to waves on the surface of the ocean, but they are in the air instead of on water. The waves are set in motion by a disturbance in the atmosphere such as a change in the wind speed or direction, a sudden updraft from a thunderstorm, or a change in the jet stream high in the atmosphere. Atmospheric gravity waves act just like the ripples around a rock thrown into a pond. Gravity keeps the waves rolling. When an atmospheric gravity wave meets a thunderstorm, it pushes down on it, which squashes it and makes it spin faster. This spinning storm is more likely to produce a tornado.
The American Geophysical Union, the American Meteorological Society, and the American Physical Society contributed to the information contained in the TV portion of this report.