The Great Wall of China was primarily built to keep out nomadic tribes, but a new study suggests constructing great walls in the American Midwest could keep out a different kind of threat – tornadoes. It might sound far-fetched, but a study conducted by Dr. Rongjia Tao from the Department of Physics at Philadelphia's Temple University suggests there is in fact some scientific merit to it. Strategically placed, 1,000 ft (300 m) high great walls could negate the forming of the destructive wind storms in Tornado Alley, and by extension, the destruction they leave in their wake.

A piece of land stretching from north to south nestled between the Appalachian and Rocky Mountain ranges, Tornado Alley is home to more than its fair share of violent weather events. According to Tao, the majority of the 811 tornadoes in the US in 2013 occurred in Tornado Alley, a result of its location in the so-called "zone of mixing."

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This is dictated by atmospheric circulation that results in a clashing of warm, northbound airflow with cold air blowing to the south. This clash results in vortex turbulence, which can then often evolve into a full-blown tornado. Tao observed that when the warm and cold air flows are each blowing at speeds of 30 mph (48 km/h) or higher, the chance of the clash resulting in a tornado was very high. Conversely, at speeds below 15 mph (24 km/h), the chance of a tornado forming was almost non-existent.

Tao's solution to obstructing these air flows is inspired by east-west mountain ranges which serve to protect the Northern and Eastern China Plains from severe tornadoes. These regions of China are also located in the zone of mixing, but suffer a much lower incidence of wind storms (just three tornadoes were confirmed in China in 2013). Tao attributes this contrast to the mountains stifling the north and south-bound flows of air.

It is the view of Tao that the effect of these east-west mountain ranges can be replicated to prevent vortex turbulence in Tornado Valley. He estimates that three great walls, each measuring 1,000 ft (300 m) high and 164 ft (50 m) wide, would be sufficient – one along the northern boundary of Tornado Alley in North Dakota, a second in the middle of Oklahoma and a third in the south, located in either Texas or Louisiana.

So is Tao's idea feasible, or is it mostly just hot air? Aesthetics aside, there are obvious implications of constructing these mega-walls. He argues that the effect on the weather would be minor, and that the walls may even serve to enhance the climate in the region. But interfering with the natural weather systems in such a way would be sure to draw its share of opposition, not unlike the idea of geoengineering the climate to mitigate impacts of global warming.

As for the cost, Tao estimates US$160 million would be required to construct each wall, though he argues this would be insignificant compared to the billions in damage caused by the regular tornadoes that strike the area.

While he doesn't anticipate the great walls being constructed any time soon, Tao is hopeful that his findings will lead to Tornado-prevention initiatives in one form or another. He suggests not-so-great walls be first built in high-risk tornado areas, and then eventually connected piece by piece until the entire region is protected. He also recommends that in the planning of any new cities in Tornado Alley, skyscrapers first be constructed along an east-west axis to serve as a protective wall and prevent tornado formation in the area.

Tao's study was supported in part by the US Naval Research Lab and the paper was published in the International Journal of Modern Physics B.

Source: World Scientific

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