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International Journal of Modern Physics B Vol. 28 (2014) 1450175 (13 pages) c World Scientific Publishing Company DOI: 10.1142/S0217979214501756 Eliminating the major tornado threat in Tornado Alley R. Tao Department of Physics, Temple University, Philadelphia, PA 19122, USA [email protected] Received 13 March 2014 Revised 25 May 2014 Accepted 27 May 2014 Published 9 June 2014 The 2013 devastating tornadoes in Oklahoma, Illinois and other states in Tornado Alley raise an important question: Can we do something to eliminate the major tornado threats in Tornado Alley? Violent tornadoes in Tornado Alley start from the clash-between northbound warm air flow and southbound cold air flow. As there is no mountain in Tornado Alley ranging from west to east to weaken or block the air flows, some clashes are violent, creating vortex turbulence called supercells. These supercells are initially in horizontal spinning motion at the lower atmosphere and then tilt as the air turns to rise in the storm’s updraft, creating a component of spin around a vertical axis. About 30% of supercells develop into tornadoes, causing tremendous damages. Here we show that if we build three east–west great walls in the American Midwest, 300 m high and 50 m wide, one in North Dakota, one passing Oklahoma to east and the third one in the south Texas and Louisiana, we will weaken or block such air mass clashes and therefore diminish the major tornado threat in the Tornado Alley forever. We may also first build such great walls locally at some areas with frequent devastating tornado outbreaks and then gradually extend them. Keywords : Tornado; turbulence-vortex; atmosphere circulation. PACS numbers: 92.60.Qx, 92.60.hk, 47.85.Gg, 92.60.kc 1. Introduction The 2013 devastating tornado attacks in Oklahoma, Illinois, and many other states in Tornado Alley remind us that tornadoes are an annually recurring threat (Fig. 1). In view of the news that these tornadoes cost many lives, and incurred damages of multi billion dollars, 1 we raise an important question: Is it possible to eliminate or at least diminish the major tornado threat in Tornado Alley? We want to emphasize that we are not talking about how to shelter us from the tornado attacks. Instead, we want to explore if there is anything we can do in order to eliminate the occurrence of major tornadoes in Tornado Alley. Some people may claim that such a question is beyond imagination as people are powerless in facing violent tornadoes. However, as will be clear in this paper, 1450175-1 Int. J. Mod. Phys. B Downloaded from www.worldscientific.com by UNIVERSITE DE SHERBROOKE on 06/24/14. For personal use only.

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Page 1: Eliminating the major tornado threat in Tornado Alley

June 9, 2014 14:19 WSPC/Guidelines-IJMPB S0217979214501756

International Journal of Modern Physics BVol. 28 (2014) 1450175 (13 pages)c© World Scientific Publishing Company

DOI: 10.1142/S0217979214501756

Eliminating the major tornado threat in Tornado Alley

R. Tao

Department of Physics, Temple University, Philadelphia, PA 19122, USA

[email protected]

Received 13 March 2014Revised 25 May 2014Accepted 27 May 2014Published 9 June 2014

The 2013 devastating tornadoes in Oklahoma, Illinois and other states in Tornado Alleyraise an important question: Can we do something to eliminate the major tornado threatsin Tornado Alley? Violent tornadoes in Tornado Alley start from the clash-betweennorthbound warm air flow and southbound cold air flow. As there is no mountain inTornado Alley ranging from west to east to weaken or block the air flows, some clashesare violent, creating vortex turbulence called supercells. These supercells are initiallyin horizontal spinning motion at the lower atmosphere and then tilt as the air turns torise in the storm’s updraft, creating a component of spin around a vertical axis. About30% of supercells develop into tornadoes, causing tremendous damages. Here we showthat if we build three east–west great walls in the American Midwest, 300 m high and50 m wide, one in North Dakota, one passing Oklahoma to east and the third one in thesouth Texas and Louisiana, we will weaken or block such air mass clashes and thereforediminish the major tornado threat in the Tornado Alley forever. We may also first buildsuch great walls locally at some areas with frequent devastating tornado outbreaks and

then gradually extend them.

Keywords: Tornado; turbulence-vortex; atmosphere circulation.

PACS numbers: 92.60.Qx, 92.60.hk, 47.85.Gg, 92.60.kc

1. Introduction

The 2013 devastating tornado attacks in Oklahoma, Illinois, and many other states

in Tornado Alley remind us that tornadoes are an annually recurring threat (Fig. 1).

In view of the news that these tornadoes cost many lives, and incurred damages of

multi billion dollars,1 we raise an important question: Is it possible to eliminate or

at least diminish the major tornado threat in Tornado Alley? We want to emphasize

that we are not talking about how to shelter us from the tornado attacks. Instead,

we want to explore if there is anything we can do in order to eliminate the occurrence

of major tornadoes in Tornado Alley.

Some people may claim that such a question is beyond imagination as people

are powerless in facing violent tornadoes. However, as will be clear in this paper,

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R. Tao

Fig. 1. The Tornado at Moore, Oklahoma, 20 May 2013.

Table 1. 2013 confirmed tornadoes in USA (enhancedFujita (EF) scale is used to rate the strength of tornadoesin USA).

Total EF0 EF1 EF2 EF3 EF4 EF5

811 413 288 79 19 8 1

Table 2. 2013 confirmed tornadoes in Europe(Fujita scale is used to rate the strength oftornadoes in Europe).

Total F0 F1 F2 F3 F4 F5

57 5 8 4 1 0 0

we believe that human beings are not powerless on this issue. In fact, if we build

three east–west great walls in Tornado Alley, we will diminish or eliminate major

tornado threat there forever.

As shown in Tables 1 and 2, in 2013, there were 811 confirmed tornadoes in USA

and 57 in Europe.2 Also in 2013, there were three tornadoes in China: two of them

were triggered by hurricanes at southeast coast area and the third one occurred in

Gaoyou, a small city with nickname “Tornado Hometown” in China.

The tornadoes in USA are much more violent than those in Europe and China.

What causes such huge differences? What can we learn from these facts? What can

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Eliminating the major tornado threat

Fig. 2. Tornado Alley is a strip of land between the Appalachian Mountains and the RockyMountains.

we do to reduce or eliminate the major tornado threat in USA? All these will be

discussed in this paper.

2. Tornado Alley, Tornado Season and Tornado Formation

In the US, most devastating tornadoes occur in Tornado Alley (Fig. 2), which

is a strip of land between the Appalachian Mountains and the Rocky Mountains,

including the northern region of Texas, Oklahoma, Kansas, Nebraska, Iowa, Illinois,

Missouri, Arkansas, Louisiana, Indiana, South Dakota, North Dakota, the eastern

edge of Colorado, the southern edge of Minnesota, the west part of Tennessee,

Kentucky, and Ohio.3–7 In 2013, among 811 confirmed tornadoes in USA, most

of them occurred in Tornado Alley. Especially, the most violent tornado outbreaks

were in Tornado Alley.

In addition to Tornado Alley, Florida, the southeastern US coast area, also has

high number and density of tornado occurrences, too. However, the tornadoes in

Florida rarely approach the strength of those that occur in Oklahoma, Kansas, etc.

Second, Florida’s high tornado frequency is credited to their almost daily thun-

derstorms, as well as many tropical storms and hurricanes that affect the Florida

peninsula. In this paper, we will concentrate on Tornado Alley.

Tornadoes in Tornado Alley have a season which tends to move northward

from late winter to mid-summer. In the Gulf Coast region, Dixie Alley refers to

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R. Tao

West Tennessee, West Kentucky, North Mississippi and North Alabama, where the

tornado season occurs in late Fall from October through December. In the Southern

states, tornado season is typically from March to May. In the Southern Plains, it

lasts from May to early June. And in the Northern Plains, Northern states and

upper Midwest, peak season is in June or July.

This information about the tornado season indicates that the occurrence of

major tornadoes in Tornado Alley is related to the clashes between the northbound

warm and moist air flow and the southbound cooler and dry air flow.8,9

From the atmospheric circulation point of view, the Tornado Alley is inside the

Ferrell cell or “zone of mixing”,10 which lies between latitudes 30◦ and 60◦.

The areas at the “thermal equator”, i.e., the sun’s zenith point, receive much

more solar energy per unit area than those at the polar region. Therefore, in the

tropic region, the sun heating the earth surface causes hot and moist surface air

to rise. The warm and moist air at high altitude flows in the poleward direction.

Due to the earth’s spin, the Coriolis force deflects the air flow to the right and

accelerates it. At about 30◦N/S latitude, it descends in a high pressure area. Some

of the descending air travels equatorially along the surface, closing the loop of the

Hadley cell and creating trade winds. However, because of the baroclinic instability,

in the middle latitudes, the “zone of mixing”, we still have strong eddies that

transport warm air poleward. In Tornado Alley, these warm and moist air flows

move from south to north, ascending and tilting to east gradually. Similarly, in the

middle latitudes, there are cold air flows from the Polar Cell moving to the south,

descending and tilting to the west gradually (Fig. 3).

At a certain season, the warm air flow front clashes with the cold air flow front

at some place in Tornado Alley. Major tornadoes in Tornado Alley all start with

such clashes. In winter, because the northbound warm air flow is weak, the clash is

Fig. 3. In middle latitudes eddies transport warm air poleward and upward and cold air equa-torward and downward.

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Eliminating the major tornado threat

(a) (b) (c)

Fig. 4. The intensive clash between the winds from the south and the winds from the north is thesource for formation of tornados in Tornado Alley. (a) Violent clash creates a vortex — supercell.(b) Tilt and updraft creates a spin about a vertical axis leading to mesocyclone. (c) Furtherstretching and strong vertical vorticity may lead to tornado.

minor and usually no major tornadoes occur in Tornado Alley. With the weather

getting warmer, the northbound warm air flow becomes stronger, the clash becomes

more and more intensified and we begin to see major tornadoes in Tornado Alley.

Especially as there is no mountain in Tornado Alley ranging from east to west to

weaken or block the air flows, some clashes are violent, creating vortex turbulence

with northbound winds near the ground and strong cold southbound winds aloft

[Fig. 4(a)]. Such violent vortexes, supercells, are initially in horizontal spinning

motion at the lower atmosphere, then tilt as the air turns to rise in the storm’s

updraft, creating a component of spin about a vertical axis [Fig. 4(b)].11 This

stage, the rotating circulation in a supercell associated with updraft, is called a

mesocyclone, which has a diameter of 5–20 km. Vortex stretching occurs in nearly

all supercells, but is not sufficient to create tornadoes. If the vortex stretching during

the vortex tilting intensifies the vertical vorticity enough to create a tornado, the

vortex size is getting much smaller as the rotation speed gets much faster. About

30% of supercells lead to tornadoes [Fig. 4(c)]. The diameter of tornadoes in the

US ranges from several meters to 4 km (Hallam, Nebraska, May 22, 2004) and they

cause tremendous damages.

The air flow clash location migrates with the season. In the winter, the thermal

equator is at 22.5◦S latitude; therefore, the cold air flow moves much further south

before meeting the warm air flow as the warm air flow has farther to travel. As the

thermal equator migrates north with the season, the air flow encounter location

in Tornado Alley is also moving to the north. This is the reason why the location

of major tornado outbreak in Tornado Alley moves with the season. Figure 5 is a

typical tornado warming map presented for weather forecast around April. When a

strong warm moist air flow comes to Tornado Alley, the violent confrontation with

the cold air flow can extend several states, making tornado outbreaks at several

places in a very short period.

Turbulence research tells us that strong vortex-turbulence in air flows must

occur near the boundary. Therefore, strong supercells must be formed near the

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R. Tao

Fig. 5. When a strong warm moist air flow comes to Tornado Alley, the violent confrontationwith the cold air flow can extend several states, making tornado outbreaks at several places in avery short period.

ground first. Although it is possible to have some vortex formed in sky, say, 300 m

above the ground, such vortex must be much weaker than the ones formed near

the ground. In addition, the air pressure on the ground is much higher than that in

high sky. Therefore, even if the vortex in sky experiences updraft, stretching and

eventually becomes a vertical vortex, it is unlikely that such vertical vortex could

descend down to touch the ground because the high air pressure on the ground

prevents it from doing so. Roughly, in order to overcome the high pressure on the

ground and push a vortex with 100 m diameter down to the ground from 300 m

sky, it would require a force of 2.99× 107 N. This is unlikely to occur.

3. Critical Wind Clash Speed for Tornado Formation

Let us find out what wind speed in clash may lead to tornadoes. The equation for

air motion is given by

ρDV

Dt= ρ

[

∂V

∂t+ (V · ∇)V

]

= −∇P + F , (1)

where D/Dt = ∂/∂t + (V · ∇), ρ is the air density, P is the pressure, F is the

viscous force and gravity force. In the polar coordinate system (r, θ, z), we have

DVr

Dt=

V 2θ

r−

1

ρ

∂P

∂r+ Fr and

DVθ

Dt= −

VrVθ

r−

1

ρr

∂P

∂θ+ Fθ . (2)

Hence we have

D(rVθ)

Dt= −

1

ρ

∂P

∂θ+ rFθ . (3)

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Eliminating the major tornado threat

Table 3. Maximum tangential velocity Vθ during air flow clash and stretching.

Wind speed(VS = VN ) Vθ with D0 Vθ with D0/2 Vθ with D0/3 Vθ with D0/4 Vθ with D0/5

15 m/s 15 m/s 30 m/s 45 m/s 60 m/s 75 m/s10 m/s 10 m/s 20 m/s 30 m/s 40 m/s 50 m/s7.5 m/s 7.5 m/s 15 m/s 22.5 m/s 30 m/s 37.5 m/s3 m/s 3 m/s 6 m/s 9 m/s 12 m/s 15 m/s

In tornado formation, the cylindrical surface with the maximum tangential ve-

locity is one of the most important surfaces. Usually, ∂P/∂θ = 0 as pressure is

along the normal direction to the surface. If the viscous force is ignored, we have

rVθ almost unchanged during the updraft and stretching. This allows us to estimate

the maximum tangential velocity Vθ.

We denote the diameter of the initial vortex as D0, the speed of south wind as

VS and the speed of north wind as VN . Then Vθ = (VS +VN )/2 initially [Fig. 4(a)].

If D0 = 300 m, VS = VN = 15 m/s, then the maximum tangential velocity of the

vortex, Vθ, will be 30 m/s as the vortex diameter is reduced to 150m during the

stretching process. This is EF0 scale tornado. When the diameter is reduced to

100 m, Vθ = 45 m/s, an EF1 scale tornado. When the diameter is further reduced

to 75 m, Vθ = 6 0m/s, an EF2 scale tornado. If the diameter is further reduced to

60 m, Vθ = 75 m/s, an EF4 scale tornado, which could cause deadly damages.

More results are in Table 3. The wind speed 7.5 m/s seems to be critical for

the tornado formation. When the wind speed is below 7.5 m/s (27 km/h), there is

almost no chance to form tornadoes. Therefore, reducing the wind speed is the key

to eliminate the formation of tornadoes.

As the major tornadoes in Tornado Alley are closely related to the warm and

cold air mass clashes, to prevent the occurrence of devastating tornadoes, we need

to eliminate such violent clashes. Is this possible? Nature actually tells us this is

possible.

4. What Can We Learn from Nature?

4.1. China

We note that the United States and China have similar geographic locations. In

particular, the Northern China Plain and the Eastern China Plain lay between

latitudes 30◦ and 45◦, similar to our Tornado Alley. However, very few violent

tornadoes occur in this region in China.

As shown in Fig. 6, in China most mountains range from west to east, while

major mountains in North America, Appalachian Mountains and the Rocky Moun-

tains, range from north to south. Mountains ranging north to south cannot block

air flows between north and south, but the mountains from east to west do. They

weaken or even block the violent clashes between the cold air flow and the warm

air flow and diminish the chance to generate devastating tornadoes.

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R. Tao

Fig. 6. The east–west mountain ranges in China eliminate the major tornado threat in theNorthern China Plain and the Eastern China Plain. Also Jiang-Huai Hills do not extend to ocean,leaving a small area unprotected, such as Gaoyou, becoming “Tornado hometown” in China.

We particularly want to point out three mountains, which seem to play the

major role in protecting the Northern China Plain and the Eastern China Plain

from tornado threats. The first one is Yan Mountain which lies at the northern

boundary of these plains. Yan Mountain is more than 300 km long and connected

to Taihang Mountains. While some peak is as high as 2000 m above sea level, most

places are 400–1000 m above sea level. Yan Mountain effectively weakens the cold

air flowing south as evidenced by the average temperature difference between the

north side and south side of the mountain. The second is Nanling (Nan Mountains),

which is about 600 km long from west to east, between 24◦N and 26◦N. Nanling

consists of five separate mountains. Between these mountains there are low hills or

valleys, which are only several hundred meters above the plain. Nanling effectively

weakens the warm air flows from south. It also blocks the hurricanes from the

ocean. Because there are no mountain ranges to connect the five major mountains

in Nanling, some cold winds are able to pass through the valleys, but violent clashes

between the cold air flow and warm air flow are effectively diminished.

The third is Qinling (Tsingling) Mountain and its east extension, the Jiang-Huai

Hills. Qinling Mountain is a long mountain ranging from west to east across China.

However, as it comes to the Northern China Plain and the Eastern China Plain, it

only consists of hills, which are about 300 m above sea level. Even so, these hills

effectively weaken the cold air flow to south and make the weather quite different

at the north side and south side of the hills. Jiang-Huai Hills stretches 800 km from

west to east.

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Eliminating the major tornado threat

We particularly want to point out that Jiang-Huai Hills do not extend to the

ocean, leaving a small area, north part of Jiangsu province unprotected. This small

area often has tornado outbreaks. For example, the city Gaoyou in this area has a

nickname “Tornado hometown”, which has tornado outbreaks repeatedly; for exam-

ple, one tornado in 2013 and another in 2011. On average, Gaoyou has one tornado

in two years. There are other small cities in this area, where tornado outbreak

occurs once in three to four years.

These facts imply that Jiang-Huai Hills are extremely effective in preventing

tornadoes from formation in their surroundings. Without Jiang-Huai Hills, a quite

big area of the plain would become “Tornado Hometown” in China.

4.2. Shawnee Hills and Ozark Mountain

While there are no mountains in the US Tornado Alley to play the same role as Yan

Mountain, Jiang-Huai Hill and Nanling in China, there are two small mountains,

Ozarks Mountains in Missouri and Arkansas and Shawnee Hills in Illinois, which

significantly reduce tornado risk for some local areas.

Ozark Mountain consists of high and deeply dissected plateaus. There are four

primary physiographic sections: the Boston Mountains, Salem Plateau, Saint Fran-

cois Mountains and the Springfield Plateau. As seen from Fig. 7, the mountain hills

are south–north ranged. Most of them have 400–500 m elevation, while some peaks

in Boston Mountains and Saint Francois Mountains have elevation about 750 m.

With Google satellite images, we have examined all these plateaus.

Fig. 7. Elevation map of Ozarks Mountains.

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R. Tao

For most parts of Salem plateau and Springfield Plateau, these north–south hills

cannot block or weaken air mass flow between north and south because the deeps

and valleys between the hills are easy for south–north air flow to pass. In fact, for

example, as Joplin faces the north–south deeps and valleys formed by these hills,

the winds get more strength as they pass these valleys and deeps, making Joplin

very high tornado risk. On the other hand, some small sections of St. Francois

Mountains and Boston Mountains have the hills east–west connected. The con-

nections seem to be 300 m above the ground. Therefore, they should be able to

block or weaken violent clashes between the cold air flow and the warm air flow in

their regions. In fact, these east–west connected sections indeed significantly reduce

tornado risks for Fayetteville, Harrison and Rolla in Arkansas and Missouri. As ana-

lyzed by www.homefact.com/tornadoes/, these cities are of low or very low tornado

risk, based on historical data with tornadoes that occurred within 30 miles of the

location. On the other hand, their neighbor cities, such as Mountain View, Joplin

and Hardy are of high risk of tornadoes because they are outside the protected zone

by these east–west connected mountain sections.

The devastating tornado outbreak in Washington County, IL on 17 November

2013 also reminds us about Shawnee Hills, which is a small mountain, 60 miles

east from Washington County, located in Southern Illinois. This small strip of land,

ranging from 5 to 40 miles wide and about 70 miles long, is characterized by higher

elevations between 120 m and 320 m. As shown in Fig. 8, most hills there are

along the south–north direction. However, some sections are east–west connected,

located at the south border of Gallatin County. Therefore, they should be able

to weaken the clashes between the cold air flow and the warm air flow in the

Fig. 8. Shawnee Hills in Southern Illinois. Some east–west connected hills are located at thesouth border of Gallatin County.

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Eliminating the major tornado threat

region. This is indeed the case. Shawnee Hills significantly reduces tornado risks for

Gallatin County. As analyzed by www.homefact.com/tornadoes/, Gallatin County

has very low tornado risk. We especially want to point out that most land in Gallatin

County is flat farm land and Shawnee Hills is just at its south boundary. On the

other hand, 60 miles west, Washington County has just suffered a horrible tornado

outbreak.

5. Conclusion: Building Great Walls to Eliminate Major Tornado

Threat in Tornado Alley

The above information is very encouraging. Although there are no mountains in

Tornado Alley to play the same role as these mountains in China, we can build

some great walls to weaken or eliminate the violent clashes between the cold air

flow and the warm air flow, hence to diminish the tornado threat. The walls should

run mainly from west to east, perpendicular to the air flows.

What height of such walls is needed to block or weaken the violent clashes

between cold air flow and warm air flow? The Jiang-Huai Hills have height of less

than 300 m above the ground, and so do many sections of Yan Mountains and

Nanling Mountains. Therefore, we estimate that the great walls should be about

300 m high from the ground. The information from Boston Mountains, St. Francois

Mountains, and Shawnee Hills also supports this estimation that a wall of 300 m

above ground will do a good job in reducing tornado risk.

How wide should the walls be? The wall height plays the most important role.

The wall width plays a secondary role. Jiang-Huai Hills have height 300 m from the

ground with their mountain tops less than 50 m wide, although the mountain base

is much wider. The man-made wall will have almost the same width from base to

top. Therefore, we estimate 50 m width should be enough for the wall. The 300 m

high wall will block air flows up to altitude of 300 m from the ground. In addition,

the wall will also provide friction for air flow just above 300 m height. The wider

the wall, the stronger the friction it provides. On the other hand, we do not want

such walls to change the weather too much. They only need to weaken the air flows

enough to eliminate the chance to produce tornadoes. Therefore, we suggest that

the great wall should be about 50 m wide.

To eliminate the tornado threat for the entire Tornado Alley, we may need to

build three great walls. The first one should be close to the northern boundary

of the Tornado Alley, maybe in North Dakota. The second one should be in the

middle, maybe in the middle of Oklahoma and going to east. The third one can be

in the south of Texas and Louisiana.

Such great walls may affect the weather, making the south side of the wall less

influenced by the north side and vice versa. On the other hand, because the walls

are only 300 m high and 50 m wide, their effect on the weather will be minor, as

evidenced by Shawnee Hills in Illinois. In fact, with scientific design, we may also

use these walls to improve the local climate.

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R. Tao

To build such great walls requires huge resources. It costs much more than

highway construction, but much less than building construction. In Philadelphia,

there is one skyscraper building, Comcast Center, just completed recently. The

Comcast Center is about 300 m high. From the cost of Comcast Center, we estimate

that to build one mile wall of 300 m height, we need about $160 million. On the

other hand, the damages caused by single tornado attack in Moore, Oklahoma on

20 May 2013 alone were multi-billion dollars. Therefore, it seems that the cost for

building such a wall is affordable.

While building the three great walls will eventually eliminate major tornadoes

in the entire Tornado Alley, it is unrealistic to expect such a huge project to start

in the near future because of the costs and other factors. On the other hand, it is

more realistic to build such great walls locally first, utilize any local natural hills

and then connect them piece by piece. For example, as Oklahoma seems to be

the state suffering from most devastating tornado attacks, we may build the first

great wall in the middle of Oklahoma and going to east. To do so locally, we must

remember that from air fluid dynamics, the area protected by the wall is roughly a

circle with the wall as its diameter (Fig. 9).

Also in developing any new city in Tornado Alley in future, we may consider

to build east–west skyscraper buildings first, then allocate the other parts of the

city surrounding the skyscraper buildings. In such a way, the skyscraper buildings

will serve as a wall, eliminating major tornado formation in their surroundings to

protect the whole city.

There is one important point we should point out here. It is well known in fluid

dynamics that for an incompressible fluid, the total flow rate is conserved because

∇v = 0. As a result, for an incompressible fluid, blocking the flow at one place will

lead the flow rate increase at other places. However, air is compressible and the

total flow rate thus is not conserved. Therefore, if the wind is blocked or weakened

by a local wall at one place, the wind velocity at other places will basically not be

affected.

Fig. 9. The area protected by a 300 m high wall is roughly a circle with the wall as its diameter.

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Eliminating the major tornado threat

From a fluid dynamics point of view, tornadoes are violent turbulences. With

the global warming, the average kinetic energy of the atmosphere is increased and

thus the average Reynolds number is going up. With higher Reynolds numbers,

more violent turbulences will occur. Therefore, tornadoes may get worse with the

global warming.

We do not expect any construction of such great walls in the near future. How-

ever, we really hope that the above discussions are convincing that eliminating

major tornadoes in Tornado Alley is not an issue beyond our imagination. In ad-

dition, we also hope that this work will stimulate much research and investigation,

such as observations,11,12 simulations13,14 and lab tests,15 leading us to a perfect

solution for this important issue: How to eliminate the major tornado threats in

Tornado Alley.

Acknowledgments

This work is supported in part by a grant from US Naval Research Lab.

References

1. For example, see, http://www.srh.noaa.gov/oun/?n=events -20130520,http://www.cnn.com/2013/11/18/us/midwest-tornadoes/ andhttp://usnews.nbcnews.com/ news/2013/10/04/20823327-tornadoes-cause-damage-injuries-across-iowa-nebraska-south-dakota

2. http://en.wikipedia.org/wiki/Tornadoes of 2013.3. H. B. Bluestein, Tornado Alley: Monster Storms of the Great Plains (Oxford Univer-

sity Press, New York, 1999).4. M. Bradford, Scanning the Skies: A History of Tornado Forecasting (University of

Oklahoma Press, 2001).5. T. P. Grazulis, it Significant Tornadoes Update, 1992–1995 (St. Johnsbury, VT: En-

vironmental Films, 1997).6. National Center for Atmospheric Research, Tornadoes. Availiable at:

http://www.ncar.ucar.edu/research/meteorology/storms/tornadoes.php (UniversityCorporation for Atmospheric Research, 2008). Retrieved on 20 November 2009.

7. T. P. Grazulis in The Tornado: Nature’s Ultimate Windstorm (University of Okla-homa Press, 2001), pp. 65–69. Available at: http://books.google.com

8. Tornado Climatology. National Climatic Data Center. January 29, 2007. Retrieved on26 April 2007.

9. S. A. Nelson, Exceptional weather — thunderstorms, tornadoes, nor’easters &drought, http://www.tulane.edu/∼sanelson/Natural Disasters/tornadoes.htm (up-dated 17-July, 2012).

10. J. Marshall and R. A. Plumb, in Atmosphere, Ocean and Climate Dynamics: An

Introductory Text (Academic Press, Boston, 2007), pp. 249–285.11. J. C. Snyder, H. B. Bluestein and V. Venkatesh, Weather Rev. 141(1), 3 (2013).12. J. L. Proud, K. K. Droegemeier and V. T. Wood, J. Atmos. Ocean. Technol. 26(3),

492 (2009).13. L. J. Wicker and R. B. Wilhelmson, J. Atmos. Sci. 52(15), 2675 (1995).14. J. Elsner, R. J. Murnane and T. H. Jagger, Math. Geosci. 45(6), 667 (2013).15. M. C. Navarro and H. Herrero, Phys. Rev. E 88, 015002 (2013).

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