Friday, February 5, 2010

Tornadoes: When Weather Gets Violent

by David DeFranza

From Toto to Twister, Storm Chasers to Greensburg, tornadoes have swept into our imaginations.

And with good reason: Every year, tornadoes in the United States cause millions of dollars in damage and lead to several severe injuries and even fatalities.

Due to urban land use practices and climate change, severe tornadoes will only become more common.

Tornadogenesis, the process of tornado formation, typically begins during a supercell, or severe thunderstorm. These storms contain a mesocyclone—a column of rotating air—that begins driving the rotation of the tornado.

As rain increases, it pulls air from the storm towards the grown. This is called the "rear flank downdraft." As this cold dry air descends, it pulls the mesocyclone towards the ground with it.

As the horizontally-rotating winds of the mesocyclone descend, they come into contact with air moving through the storm intake. This causes the horizontal wind to tilt and become vertical. This transition typically forms a large "wall cloud."

When the warm, moist, air of the updraft mixed with the cool, dry, air of the rear flank downdraft, cloud formation is intensified. In addition, the downdraft focuses the base of the mesocyclone, causing it to pull air from a smaller area.

Once this base is focused, the updraft intensifies dramatically, lowering the air pressure on the ground and pulling the mesocyclone closer to the surface. This creates the funnel cloud and marks the point at which a true tornado has formed.

Though it generally requires this specific interaction of air currents, tornadoes have been known to form over a wide-range of terrains during all seasons of the year. They have even been known to form and travel over water.

These waterspouts look like they suck water up into the atmosphere but in reality, the water visible in the column is storm condensation.

A common myth associated with tornadoes is that their size is relative to their severity. While there is an observed trend that massive wedge-shaped tornadoes have caused more damage, this is certainly not a rule. Historically, skinny "rope" tornadoes have been some of the most damaging.

Tornadoes are classified, in fact, by the amount of damage the cause. The most commonly used metric is the Fujita Scale—or the updated Enhanced Fujita Scale—which measures a tornado's ability to cause damage to human-built structures and vegetation.

At the bottom of the scale, EF0 tornadoes may only be able to damage trees while EF5 tornadoes, at the top of the scale, can pull buildings from their foundations and even deform skyscrapers.

There should be a separate category, however, for tornadoes like the one encountered by high school senior Matt Sutter on March 16, 2006.

The tornado pulled Matt from his home and carried him 1,307 feet. Though he had been knocked unconscious by a blow to the head second before liftoff, Matt survived.

Scientists know that pollution can increase the severity of thunderstorms, and thus tornadoes, but what factor does climate change play?

Some researchers believe that the increase of carbon and moisture in the atmosphere indicates that there is simply "more energy" there, making all kinds to powerful climate events more likely.

For whatever reason, the frequency and severity of tornadoes has increased and, even if thunderstorms become less common, an almost guaranteed increase in storm intensity will make tornadoes even more likely.

So much of the research and documentation of tornadoes focuses on the obvious destruction they cause; the danger they pose to people's lives and livelihoods. But, as with every storm, there is usually a silver lining.

Whether it is new technology for harnessing the power of a tornado or the story of a community using a disaster as an opportunity to build a better life, such positive actions help us step back and, from a safe distance, appreciate tornadoes for what they are: Powerful testaments to the intricate beauty of nature.

...view Tornado slideshow at

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