What is a tornado?

brief introduction

The fastest and fiercest strong wind on the earth: tornado (tornado phonetic symbol: [t? :' neid？ U]) Tornado [1] is a strong small-scale air vortex, which is formed by two air streams moving in opposite directions and rubbing against each other in extremely unstable weather. This vortex causes the air pressure in the center to be very low, and objects on the ground are sucked up and thrown into the sky ... The shape of the tornado is very strange. Its upper part is black or thick gray cumulonimbus clouds, and its lower part is a funnel-shaped cloud column hanging like an elephant's nose. The wind speed is generally 50 meters per second to 100 meters, and sometimes it can reach 300 meters per second.

tornado

Strong cyclone produced by funnel-shaped clouds (tornadoes) extending from the bottom of thunderstorm clouds to the ground, with wind power of more than12m and maximum of more than100m per second, usually accompanied by thunderstorms and sometimes hail.

Attracted by the extremely low air pressure in the center of the tornado, the air rotates rapidly around the axis of the tornado. In the thin layer of air tens of meters thick near the ground, the airflow is sucked into the bottom of the vortex from all directions, and then becomes a vortex around the axis. The wind in a tornado is always cyclonic, and the air pressure in its center can be 10% lower than that around it.

A tornado is a strong wind vortex accompanied by a funnel-shaped cloud column rotating at high speed. The wind speed near the center can reach 100 m/s ~ 200 m/s, with a maximum of 300 m/s, which is several times larger than the maximum wind speed near the center of typhoon (generated at sea). The central air pressure is very low, generally as low as 400 hectopascals and as low as 200 hectopascals. It has a great sucking effect, which can suck the sea (lake) water away from the sea (lake) surface, form a water column, and then connect with the clouds, commonly known as "dragon water absorption". Because the air inside the tornado is extremely thin, the temperature drops sharply and the water vapor condenses rapidly, which is an important reason for the formation of funnel cloud column. The average diameter of the funnel cloud column is only about 250 meters. Tornadoes are produced in very unstable cumulonimbus clouds. Its formation is related to the strong rise of warm and humid air, the southward movement of cold air and topography. Its life history is short, usually lasting ten minutes to an hour or two, but its destructive power is amazing. It can uproot trees, blow down buildings or roll some ground objects into the air. There are tornadoes in Jiangsu Province almost every year, but the location has no obvious regularity. It usually appears in June and July, sometimes in early or middle August. Tornadoes form "dragon water absorption" on the water surface.

In midsummer, there is a tornado at sea. When listening to the typhoon weather forecast, you can often hear the words "typhoon center wind 12 above". It seems that "12" is the best wind. Is there a stronger wind in nature? Yes, it was a tornado.

Tornadoes, commonly known as "dragons suck water", may be named because their funnel-shaped cloud columns look like mythical "dragons" falling from the sky and sucking water into the air. In fact, it is a strong wind vortex with small range and strong wind force extending from the bottom of thunderstorm cloud to the ground or water surface.

Tornado winds are very strong. Near the tornado center, the horizontal wind speed can reach more than 100 meters per second, and in extreme cases it can reach 300 meters. 12 wind speed is equivalent to more than 30 meters per second, which is naturally not as good as a tornado. The damage caused by such a rare huge wind force is amazing. When it touches the ground, it can throw people and animals into the air like a joke, and then throw them down. It can "pull up weeping willows", destroy buildings and even cut off a corner of a solid tall building like a sword. On September 24th, 1956, a tornado appeared in Shanghai. It actually lifted a three-or four-story 1 10 ton oil storage tank into the air of 15 meters, and then threw it away from 100 meters. During 1925, a powerful tornado occurred in the United States, causing more than 2,000 casualties. Why is the tornado so strong? The main reason is that a large amount of air escapes in the tornado, which makes the air in the center of the tornado very thin and the air pressure is very low, which is particularly different from the air pressure in the periphery. The air difference between the typhoon center and the periphery is 20 millibars per 100 km on average, while the air difference between the tornado center and the periphery is 20 millibars as long as it is 20 meters. The greater the pressure gradient, the greater the wind force. No wonder tornadoes are many times stronger than typhoons. The area covered by the tornado is very small. 1927 A tornado in North Carolina, USA, in which trees were uprooted within 15 square meters, is safe near the tornado.

form

Tornadoes are a natural phenomenon and the product of thunderstorms in the clouds. Specifically, a tornado is a form in which a small part of the huge energy of a thunderstorm is released in a small area. The formation of tornadoes can be divided into four stages:

(1) The instability of the atmosphere produces a strong updraft, which is further strengthened due to the influence of the maximum transit airflow in the rapids.

(2) Due to the interaction with the wind with shear speed and direction in the vertical direction, the updraft starts to rotate in the middle of the troposphere, forming a mesoscale cyclone.

(3) With the development and upward extension of mesoscale cyclone to the ground, it becomes thinner and stronger. At the same time, a small area to strengthen cooperation, that is, the primary tornado is formed inside the cyclone, and the same process of producing the cyclone forms the tornado core.

(4) The rotation in the tornado core is different from that in the cyclone, and its intensity is enough to make the tornado extend to the ground. When the developing vortex reaches the ground, the ground air pressure drops sharply and the ground wind speed rises sharply, forming a tornado.

Tornadoes often occur in thunderstorm weather in summer, especially in the afternoon to evening. The attack range is small, and the diameter of tornadoes is generally between ten meters and several hundred meters. The survival time of tornadoes is generally only a few minutes, and the longest is no more than a few hours. The wind is particularly strong, and the wind speed near the center can reach 100-200m/s, which is extremely destructive. Where tornadoes pass, trees are often pulled up, vehicles are overturned, buildings are destroyed, and sometimes people are sucked away, which is very harmful.

trait

outfall

Tornado is the strongest vortex phenomenon in the atmosphere. Although its influence is small, it is extremely destructive. It often destroys crops and tens of thousands of fruit trees in an instant, interrupts traffic, collapses houses and loses human and animal lives. The horizontal range of tornadoes is very small, ranging from several meters to several hundred meters in diameter, with an average of about 250 meters and a maximum of about 1 km. The diameter can reach several kilometers in the air, and the maximum is 10 km. The maximum wind speed can reach 150 km to 450 km per hour. Tornadoes usually last only a few minutes, and the longest is only a few minutes, but the disaster caused is very serious.

Tornadoes often occur in thunderstorm weather in summer, especially in the afternoon to evening. The attack range is small, and the diameter of tornadoes is generally between ten meters and several hundred meters. The survival time of tornadoes is generally only a few minutes, and the longest is no more than a few hours. The wind is particularly strong. It is extremely destructive. Where tornadoes pass, trees are often pulled up, vehicles are overturned, buildings are destroyed, and sometimes people are sucked away, which is very harmful.

type

1. Real tornado

(1) A multi-vortex tornado refers to a tornado with more than two eddies rotating around the same center. Multi-vortex structures often appear in violent tornadoes, and these small vortices often cause greater damage in the area where the main tornado passes. ② waterspout (or watersuput, English). It can be simply defined as a water tornado, usually referring to a non-supercell water tornado. Waterspouts may appear in oceans and lakes all over the world. In the United States, waterspouts usually occur on the southeast coast of the United States, especially in southern Florida and the Gulf of Mexico. Although waterspout is a kind of tornado by definition, its destructive power is less than that of the most powerful grassland tornado, but it is still quite dangerous. The hose will overturn the ship and destroy it. When it lands, it will do more harm and take away life. When waterspouts may be produced or are already visible in coastal waters, the National Weather Service often issues special maritime warnings or tornado warnings when waterspouts will move to land. Dragon absorbs water: another name for tornado. Tornado got its name because it is very similar to the East China Sea Horned Dragon in breaking the waves in ancient mythology. It also has many aliases, such as "dragon absorbs water", "dragon wags its tail" and "upside down dragon". Tornadoes are water-absorbing dragons, which are common tornadoes on land. Tornadoes are the flow of air, and air is invisible. We can only see it because the air pressure in the center of the tornado is very low and attractive. Attract dust, water vapor and other sundries. So we can see the outline of the tornado. If a tornado moves on the water, the center of the tornado will suck water into the sky like a syringe. Due to gravity, liquid water cannot stay in the air for a long time. So after the dragon absorbs water, the water sucked into the sky will fall down. It formed rain, which was a heavy rain. So the so-called dragon water absorption is a tornado. The dragon absorbs water, which vividly describes this phenomenon.

Shenzhen Shekou Shuanglong water absorption

Dragon suction is a tornado that occasionally appears over warm water. Its upper end is connected with thunderstorm clouds, and its lower end directly reaches the water surface, rotating and moving at the same time. This is a vortex, and the air rotates rapidly around the axis of the tornado. Attracted by the extremely low air pressure in the center of the tornado, the water flow is sucked into the bottom of the vortex and then becomes a vortex around the axis. Tornadoes roll water from lakes or oceans into the air, forming a high water column. Like being sucked into the air, the water in the water column is commonly called "dragon water absorption" or "tornado water". From a distance, the water column swept into the air by a tornado is not only like a python dangling in the air, but also like the nose of an elephant that keeps swinging. On September 3, 2007, the "Dragon Sucking Water" spectacle appeared in Xingyun Lake in Jiangchuan, which was reported by the media and attracted wide attention from all walks of life. Villagers along the lake generally believe that "dragon absorbs water" is a common natural phenomenon, which has been rainy for many years, but there are also some mysterious phenomena that are difficult to explain. Li Jiangui, a villager from Shiyanshao Village, Luju Town, Jiangchuan County, started fishing at the age of six or seven. He is 47 years old. He told the author that he had seen too many phenomena of "dragons absorbing water", but such a magical landscape on September 3 was rare.

On August 3, 2009, the landscape of "dragon absorbing water" appeared on Changchun Lake in Qixia City. On the same day 16, a towering water column suddenly rose on the lake in Changchun, and it rained cats and dogs instantly.

At 7: 30am on June 4th, 2009, at 10, a spectacular sight of three dragons sucking water appeared in Bohai Bay. They suck a lot of seawater into the air, and then bring thunderstorms.

Bohai bay dragon absorbs water

At 9: 30 in the morning of August 23, 2009, when I went to Erhai Lake, the weather suddenly changed, the water was covered with dark clouds, and a water column was connected between the sea and the sky like a black dragon. Due to the vigorous development of cumulus clouds over Erhai Lake, the up-and-down convection movement intensifies and the temperature difference increases, forming this spectacle.

20 10 at 9 o'clock in the morning on July 27th, a rare tornado appeared in the sea between Hong Kong and Shenzhen, forming three rare dragon-sucking landscapes on the sea surface.

On the morning of September 6, 2065438+00, in the intermittent rain, a "dragon" fell into the lake from the boundless sky ... This story that sounds like a myth really happened in Qinghai Lake, which is located on the Qinghai-Tibet Plateau, with an altitude of 3200 meters. On September 1 day, the meteorological landscape of dragon water absorption appeared twice in Qinghai Lake, and the plateau Shenhu Lake added more exotic colors.

(3) landspout (called dust tube tornado by the National Weather Service) is a term used to describe tornadoes unrelated to mesoscale cyclones. Tornadoes and waterspouts have some similar characteristics, such as relatively weak intensity and short duration, and funnel-shaped clouds formed by condensation often do not touch the ground. Although the intensity is relatively weak, tornadoes will still bring strong winds and serious damage.

(4) Fire tornado, a very rare tornado, is a combination of tornado and flame. Brazilian tornado.

[2]2065 438+00 Brazil, located in the southern hemisphere, suffered from a rare drought and little rain, and many places in the country ignited mountain fires. On August 24th, a tornado blew at a fire spot in Sao Paulo, Brazil, forming a rare fire tornado landscape. The tornado rolled up a flame several meters high and spun like a giant fire dragon. This "Dragon Wind" was taken on the 24th. "Fire Dragon" flew several meters in the burning field, blocking a road. In order to put out this "fire dragon", local helicopters were dispatched. It hasn't rained for three months in the area with "Dragon Wind". Unusually dry weather and strong winds contributed to the fire here. Brazil's Global TV reported that the air dryness in Sao Paulo has caught up with the Sahara desert.

Tornado at sea

Tornadoes are classified by Fujita series, which was put forward by Japanese-American meteorologist Fujita Tetsuya in 197 1 year. F0 wind speed

The degree of damage is serious. The performance is as follows: the roof walls of stronger houses have been scraped off, trains have derailed or overturned, and most trees in the forest have been uprooted. Heavy vehicles scrape off the ground or escape. Grade F4 wind speed is 207–260mi/h 93–116m/s, and the occurrence probability is 2%. The performance is as follows: if the foundation of a solid house is not very solid, it will explode to a certain distance, and the car will explode like a missile. The F5 wind speed is 261–318m/h17–141m/s.

counter-measure

(1) At home, be sure to stay away from doors, windows and external walls of houses and hide in the wall or small room opposite the tornado. The safest place to avoid a tornado is the basement or semi-basement. Tornado, magical nature

(2) In case of emergency such as pole collapse and house collapse, the power supply should be cut off in time to prevent electric shock or fire. (3) When there is a tornado outside the venue, you should look for low-lying land nearby, but stay away from trees and telephone poles to avoid being smashed, crushed and electrocuted.

(4) When the car encounters a tornado when going out, you must not drive to avoid it, nor do you avoid it in the car, because the car has almost no defense ability against tornadoes. You should leave the car immediately and avoid it in a low-lying place. 1On May 27th, 999, four counties in central Texas, including Austin, the capital, were hit by a huge tornado, killing at least 32 people and injuring dozens. It is reported that in jarrell, 40 miles north of Austin, more than 50 houses collapsed and more than 30 people were killed in the tornado. The damaged area is 1 mile long and 200 yards wide. This is another tornado area in the United States after Miami was hit by a tornado on May 3, 65438. Generally speaking, a tornado is a whirlwind. When it touches the ground, its diameter ranges from several meters to 1 km, with an average of several hundred meters. Tornadoes range from a few meters to dozens of kilometers, and things are robbed everywhere. The funnel-shaped center of tornado is composed of inhaled dust and condensed water vapor, which is a visible "dragon mouth". On the ocean, especially in the tropics, similar scenes are called sea tornadoes.

Tornado in sandbar

Most tornadoes rotate counterclockwise in the northern hemisphere and clockwise in the southern hemisphere, with some exceptions. The exact mechanism of tornado formation is still under study, and it is generally believed to be related to the violent activities of the atmosphere.

Since19th century, the accuracy of weather forecast has been greatly improved, and various disasters and storms such as tornadoes and hurricanes can be detected by weather radar.

Tornadoes are usually extremely fast, and it is not surprising that the wind speed is 100 meters per second, even reaching more than 175 meters per second, which is five or six times larger than the typhoon 12. The range of wind is very small, generally the diameter is only 25~ 100 meters, and only in rare cases can the diameter reach more than one kilometer; It takes only a few minutes from occurrence to disappearance, at most a few hours.

Tornadoes are also very powerful. There was a tornado 1956 in Shanghai on September 24th. It easily lifted a large oil storage barrel weighing 220,000 Jin to the altitude of15m, and then threw it away from120m.

1879 at 4 pm on may 30, two dark and thick clouds were merging over northern Kansas. After 15 minutes, a vortex was generated at the lower end of the cloud. The vortex has grown rapidly and become a huge pillar of indomitable spirit. Within three hours, it ran wild all over the state like a dragon, and no one was spared wherever it went. However, the strangest thing happened at the beginning, when the tornado whirled across a small river and met a cliff. Obviously, it is impossible to surpass this obstacle, so the vortex turns to the west, and there happens to be a newly built 75-meter-long railway bridge over there. The tornado vortex actually pulled it down from the stone pier, twisted it a few times, and then threw it into the water.

correlation detection

Tornadoes have long been a mystery, and it is for this reason that it is necessary to understand them. The tornado struck suddenly and violently, and the wind force produced was the strongest on the ground. Because of its suddenness and dispersion, it is difficult to observe it effectively. What is the wind speed of a tornado? No one really knows, because the time from the occurrence to the dissipation of tornadoes is very short and the area of action is very small, so that the existing detection instruments are not sensitive enough to accurately observe tornadoes. Relatively speaking, Doppler radar is an effective and commonly used observation instrument. Doppler radar aims at the microwave beam emitted by the tornado, and the microwave signal is reflected by the debris and raindrops in the tornado and then received by the radar. If the tornado is far away from the radar, the frequency of the reflected microwave signal will move to the low frequency direction; On the contrary, if the tornado gets closer and closer to the radar, the reflected signal will move to the high frequency direction. This phenomenon is called Doppler frequency shift. After receiving the signal, the radar operator can calculate the speed and moving direction of the tornado by analyzing the frequency shift data.