The disaster blockbuster "Tornado" was recently released simultaneously in North America and the mainland. Hollywood blockbusters are well-made, with stunning special effects and tight pacing, and the viewing experience is "naturally excellent".
However, the background knowledge of tornadoes in the film is slightly insufficient, and the relevant plot may be a little confusing for non-meteorological audiences. Therefore, friends who plan to watch the movie, you may wish to use this article as a guide to watching the movie, so that you can enjoy the visual feast at the same time, you can also gain full scientific knowledge!
As soon as the film opens, the protagonists are engaged in an intense scientific experiment in which they try to introduce a super-absorbent polymeric material into the tornado, imitating the way diapers absorb water and weaken the tornado by reducing the amount of water vapor in the atmosphere. However, is the reality really that simple?
To make a scientific judgment on this issue, we must first have a basic understanding of tornadoes.
Without thunderstorm clouds, there are no tornadoes
In meteorology, a tornado is defined as an intense, small-scale air vortex that is a strong cyclone produced by funnel-shaped clouds that extend from the base of a thunderstorm cloud to the ground.
Tornado formation (Image source: Wallpapersden)
Tornadoes never appear in calm scenes, they always "appear" under overwhelming thunderstorm clouds, and their terrifying sights are shocking to the body and mind. And the thunderstorm clouds that give birth to tornadoes are also known as "mother clouds", so without thunderstorm clouds, tornadoes have nowhere to grow.
Thunderstorm clouds are created in the presence of strong convective activity in the atmosphere. Convective activity in the atmosphere can be simply understood as the rise of warm air and the sinking of cold air. Among them, during the rise of warm air, the water vapor carried by the warm air will undergo phase changes due to the drop in ambient temperature, and the liquefaction and condensation from gaseous water to water droplets and ice crystals will form cumulonimbus clouds and produce weather phenomena such as precipitation. Under strong convective activity, the cumulonimbus cloud will further develop into its "Pro" version, a thunderstorm cloud with lightning and thunder.
Thunderstorm clouds with lightning and thunder (Image Credit: GetWallpapers)
In order for strong convection to occur in the atmosphere, the following three conditions need to be met at the same time: first, it has unstable atmospheric stratification conditions with warm and humid lower layers and dry and cold upper layers; Second, there are sufficient water vapor conditions in the lower layers of the atmosphere, which is a necessary "fuel" for convective activities. The third is the existence of an uplift trigger mechanism, which triggers the onset of convective activity. When these three conditions are met at the same time, severe convective weather is imminent, and thunderstorm clouds can form in a short period of time.
In thunderstorm clouds, the vertical change in horizontal wind speed and direction (i.e., vertical wind shear) is significant. This change causes the air flow to rotate as it rises, creating a horizontal vortex, just as we would place our hands up and down and rub the plasticine in different directions to shape it into long strips. At the same time, due to the uneven strength of the updraft, the rise is strong in some places and weak in others, resulting in the tilt of the vortex tube when it rotates. A mesoscale vortex is formed when one end of the vortex extends under the cloud base, and once the mesoscale vortex is grounded, it means that the tornado has officially formed.
How tornadoes are formed (Image source: eschooltoday)
Therefore, there are two key steps to determine whether a tornado can form: first, whether there will be strong convective weather in the atmosphere, and second, whether the vertical change of wind speed in the thunderstorm cloud can meet the conditions for the formation of tornadoes. But which thunderstorm cloud can breed tornadoes is still a big problem for the scientific community.
United States has a "tornado corridor"
Tornadoes, a violent vortex in the atmosphere, are like a twitching spinning top, and the plains are the best stage for it.
On the mainland, tornadoes favor the eastern plains of the continent, especially the middle and lower reaches of the Yangtze River. The frequency of tornadoes gradually decreases from the eastern coast to the western inland, with Jiangsu and Guangdong having the most tornadoes, with an average of 4.8 and 4.3 tornadoes per year, respectively.
From a global perspective, the mid-latitudes are the main stage for tornadoes, with annual tornado activity occurring in North America, Europe, Russia, China, Japan and Australia. Among them, the United States is known as the "Tornado Kingdom" with up to 75% of the world's tornadoes every year. Based on statistics from 2000-2020, United States recorded an average of 1,141 tornadoes per year.
The vast majority of tornadoes in the United States occur in the central Great Plains, known as the "Tornado Corridor." This corridor runs from United States Texas to the north to the Canada, and its west side is affected by the Rocky Mountains, and the airflow is easy to form an unstable atmospheric stratification of "high level cold and low layer warm" after the air flow passes over the mountains, and with the cold air from the north of the Canada and the warm and humid air from the Mexico bay, it is very easy to form an unusually strong convective weather system such as strong winds, heavy rain, hail and tornadoes in the broad central plain. Because of this, the "Tornado Corridor" has not only become a hot spot for meteorologists, but also an ideal setting for the "Tornado" movie, where most of the inspiration for the shocking tornado scenes on the screen came from this "cradle" of tornadoes.
Schematic diagram of the mechanism of tornado formation in the tornado corridor United States, and the red shaded area is the location of the tornado corridor (Source: wordpress, the author of this article is Chinese)
Shockingly, on December 10, 2021, 61 tornado "collective shows" were staged in this corridor at the same time in a short period of time, bringing unprecedented threats and challenges to the surrounding residents.
Satellite image of central United States on December 10, 2021, with bright blue light indicating observed tornadoes (Image source: NOAA)
How can you tell how destructive a tornado is? This index is needed
The impact of a tornado is like a giant vacuum cleaner. The winds in tornadoes are surprisingly fast, with NOAA weather researchers reporting the most powerful tornadoes with winds exceeding 483 kilometers per hour. You must know that on April 21, 2022, the two "Fuxing" trains in mainland China set a new world record of 870 kilometers per hour for the relative rendezvous of high-speed rail EMUs, and the speed of a single train was only 435 kilometers per hour. It is conceivable that such a high wind speed in a tornado can tear objects apart in an instant. Strong winds give tornadoes a strong suction. Bernoulli's equation tells us that when the wind speed increases, the air pressure decreases. As a result, the central air pressure of the tornado, which rotates at high speed, is much lower than the surrounding air, creating a huge pressure difference that sucks the surrounding objects into it.
Surface pressure distribution of a tornado in Manchester, South Dakota, June 2003 (Image source: Prevatt et al., 2012)
How is the power of a tornado measured? Internationally, the wind speed and destructive power are mainly considered, and the enhanced Fujita Index (EF level) is used to rate tornadoes. This standard was established by Tetsuya Fujita, a Japanese-American scientist who dedicated his life to solving the mystery of tornadoes. There are 6 levels of EF from 0 to 5, each corresponding to a different wind speed and degree of damage. Like what:
- EF0: Wind speed less than 33 m/s, minor damage, such as broken branches.
- EF1: Wind speed 33-49 m/s, moderate damage, roof material may be lifted.
- EF2: Wind speed 50-69 m/s, large damage, wooden roofs, walls may be blown away.
- EF3 and above: The wind speed is higher, the destructive power is great, and heavy vehicles can be blown away!
The process of grading a tornado is very complex, requiring a comprehensive judgment of multiple information such as on-site investigations, meteorological observation data, satellite and radar images, etc. When an incident occurs, meteorological services and disaster assessment agencies act quickly to collect data and assess and grade them against the standards.
The strongest tornado recorded on the mainland was EF4, which occurred in Funing, Jiangsu Province in June 2016. EF5 tornadoes are extremely rare, and tornadoes may not occur once a year in the United States. The most recent EF5 tornado dates back to May 20, 2013, when a deadly tornado struck Oklahoma in United States, killing at least 24 people and causing property damage estimated at more than $3.5 billion.
How to forecast a tornado?
With the current state of technology, forecasting tornadoes remains a global problem.
First of all, our observation network is too "rough". The spatial scale of severe convection and tornadoes is small, for example, the average scale of tornadoes is only about 100 meters, while the average distribution distance of continental automatic weather stations is tens of kilometers. Using such an observation net to monitor tornado activity is like using a large net to catch small fish, and the difficulty of "catching" can be imagined. Besides, tornadoes come and go in a hurry, with an average life cycle ranging from a few minutes to no more than an hour, and disappearing without a trace before people can learn more about it. In addition, tornado formation involves multiple complex meteorological factors and interactions, which interact with each other and are unpredictable, making tornado formation and development unpredictable and difficult to predict.
Accurately forecasting a tornado is a challenge of time and intelligence. Under certain conditions, when a strong thunderstorm cloud appears, the Meteorological Bureau will send a Doppler radar vehicle or a mobile meteorological observation station to the scene of the thunderstorm cloud for on-the-spot observation. A mobile meteorological observatory is a portable meteorological monitoring device that integrates a variety of meteorological sensors. It can monitor meteorological elements such as wind speed, wind direction, temperature, humidity, and air pressure in real time, and transmit the data to the meteorological center or relevant departments through wireless communication, so as to make judgments on the future activities of tornadoes.
Mobile weather observatory monitoring tornadoes (Image source: NOAA)
At present, our forecast of severe convective weather can be two hours in advance, and the forecast of tornadoes, the world's most advanced forecast United States, can only be forecast 10-15 minutes in advance, although the time is not long, but it is enough for people to take corresponding evacuation measures.
When it comes to tornado forecasts, it's better to trust them than to gamble with your own life. In recent decades, thanks to the development of Doppler radar and the improvement of computer models, the United States has issued early warnings for about 87% of deadly tornadoes between 2003 and 2017, improving the public's ability to respond to tornado disasters.
The average annual tornado forecast lead time in the United States is 11.6 minutes (Image source: AGU)
Will humans be able to "wipe out" tornado activity?
Through a variety of research methods such as field observations, laboratory simulation experiments and computer numerical simulations, people have a deeper understanding of the mechanism of tornadoes' occurrence and disappearance. So, based on the existing knowledge, can humans intervene in tornado activity?
From the theoretical level, there is indeed a possibility of influencing tornado activity, and the core of it lies in intervening in the key atmospheric conditions required for tornado formation, such as warm and humid airflow, vertical wind shear, etc. Theoretically, by adjusting these conditions, the generation and development of tornadoes can be affected to a certain extent. In addition to the idea of reducing the amount of water vapor in the atmosphere of the tornado by placing strong water-absorbing substances in the tornado's pathway, there are more radical ideas, such as the use of explosive missiles to alter the vertical wind shear environment, or to directly interfere with the structure of the tornado's airflow that has already formed.
However, there are many challenges in putting these theoretical ideas into practice. First, there is a huge uncertainty between the feasibility of the technology and the actual effect. Atmospheric systems are complex and volatile, and human intervention can have unpredictable consequences and may even exacerbate disasters rather than mitigate their effects. Second, from a cost-benefit perspective, these methods are costly and unlikely to yield significant results and, more critically, such high-risk operations in populated areas, such as missile launches, directly threaten public safety and could lead to new catastrophic consequences. In addition, tornado activity is highly sudden and transient, and how to accurately judge and effectively implement intervention measures in a short period of time is also a huge problem.
Although it is not yet possible to directly "domesticate" tornadoes to eliminate their destructive power, scientists and engineers have begun to explore how to "harness" the enormous energy contained in tornadoes to some extent to bring clean, efficient energy solutions to human society. By simulating the principles of tornado formation, attempts are made to create powerful tornado-like air currents in a controlled environment, and then use the kinetic energy in these air flows to convert into electrical energy. The Mercedes-Benz Museum in Stuttgart, Germany, has the "world's most powerful artificial tornado" device, with a height of 34.13 meters, although its main function is not for energy generation, but its successful simulation of such a huge tornado undoubtedly provides strong practical support and technical verification for the idea of "artificial tornado" energy power generation.
The world's largest man-made tornado (Image Credit: Pinterest)
In the face of the threat of tornadoes, human beings are still too small, and like the protagonists in the film, we should keep in mind the three-character evacuation principle of "hide, escape, and lie down":
1. Duck first: Unlike other severe convective weather, the best response strategy when a tornado is spotted. If conditions allow, hiding in the basement will be the safest option.
2. Flee in the opposite direction: When encountering a tornado in the wild, quickly move in the opposite direction or vertical direction of the tornado's advance to seek evasion. Remember to avoid hiding in dangerous areas such as garages, wooden buildings, etc.
3. Find low-lying areas to lie down: If a tornado is approaching, immediately find low-lying terrain to lie down, lower your center of gravity, grasp a firm object, close your mouth and eyes, and protect your head with both hands and arms to prevent being hit by flying objects.
References:
[1] Xu Beilei, Zhao Shihao, Qiu Penghui, et al. Building Structures, 2024, 54(2):110-114.
[2] Prevatt D O , Lindt J W V D , Back E W ,et al. Making the Case for Improved Structural Design: Tornado Outbreaks of 2011[J]. Leadership & Management in Engineering, 2012, 12(4):254-270.DOI:10.1061/(ASCE)LM.1943-5630.0000192.
[3] http://qxqk.nmc.cn/html/2021/11/2021
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[4] https://eschooltoday.com/learn/how-do-tornadoes-form/
[5] https://commons.wikimedia.org/wiki/
File:Nssl0311_-_Flickr_-_NOAA_Photo_Library.jpg
[6] https://blogs.agu.org/wildwildscience/
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[7] https://www.pinterest.com/pin/the-worlds-strongest-manmade-tornado--363243526165025730/
[8] https://www.thepaper.cn/newsDetail_
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Author: Chen Kexin
Institute of Atmospheric Physics, Chinese Academy of Sciences