What is a tornado?

Now we know that a tornado is a violently rotating circular column of air. Its upper end is connected to the thundercloud, and some of its lower ends are suspended in mid-air, and some extend directly to the ground or water. Rotate and move forward. A tornado that occurs at sea, like a "dragon sucking water", is called a "waterspout"; a tornado that appears on land, stirs up dust, and sweeps away houses, trees, etc., is called a "landspout." From a distance, it not only looks like a giant python hanging in the air, but also like an elephant trunk that keeps swinging.

How is this big "elephant trunk" formed?

A tornado in nature is born in a thundercloud. In thunderclouds, the air is very turbulent and the temperature difference between the upper and lower parts is huge. On the ground, the temperature is in the twenties degrees Celsius, and the higher you go up into the sky, the cooler the temperature becomes. At an altitude of more than 8,000 meters above the top of the cumulonimbus clouds, the temperature is as low as minus 30 degrees Celsius. In this way, the cold air above falls rapidly, and the hot air below rises violently. When the updraft reaches high altitude, if it encounters a strong horizontal wind, it will force the updraft to "hang upside down" (rotate downward). Due to the alternating disturbance of the upper air, rotation occurs and many small vortices are formed. These small vortices gradually expand. The up and down agitation became more and more intense, and finally formed a large vortex. The large vortex first rotates around the horizontal axis, forming a horizontal column of air rotation. Then, the two ends of this air rotating column gradually bent, and slowly hung down from the bottom of the cloud. Regarding the direction in which cumulonimbus clouds advance, the cloud body extending from the left is called a "left tornado", and the cloud body extending from the right is called a "right tornado"; the former rotates clockwise, and the latter rotates counterclockwise. The one that reaches the ground is usually the right tornado, and there are few chances for the left tornado to reach down.

In addition, tornadoes are also prone to occur at the intersection of two squall lines. Squall lines often appear at the outpost of strong cold air during hot seasons.

When a tornado appears, there is often more than one. Sometimes two or even more "elephant trunks" - funnel cloud pillars - can appear from the same cumulonimbus cloud. It's just that some "elephant trunks" have just begun to extend downward, while the lower ends of some "elephant trunks" have already touched the ground or are retracting into the clouds after touching the ground, and some are stretching and contracting at the bottom of the clouds but never hanging to the ground.

The range of tornadoes is small, with an average diameter of 200-300 meters; the smallest diameter is only a few tens of meters, and only a handful of large ones reach more than 1,000 meters in diameter. Its life is also very short, often only a few minutes to dozens of minutes, no more than a few hours at most. Its moving speed averages 15 meters per second, and the fastest can reach 70 meters; the length of its moving path is mostly about 10 kilometers, with short ones only tens of meters and long ones up to hundreds of kilometers. The width of the ground where it causes damage is generally only 1-2 kilometers.

Tornado has an extremely rough temper. Wherever it went, the roar was like thunder, as strong as a fleet of airplanes passing by at low altitude. This may be due to the fact that the wind speed exceeds the speed of sound in some parts of the vortex, thus generating a small amplitude shock wave. How fast are the winds in a tornado? It cannot be measured yet, because no anemometer can withstand its destruction. Under normal circumstances, the wind speed may be 50-150 meters per second. In extreme cases, it may even reach 300 meters per second or exceed the speed of sound.

Supersonic wind energy can produce infinite power. In 1896, a pine stick carried by a tornado in St. Louis, USA, penetrated a one-centimetre-thick steel plate. In 1919, a tornado in Minnesota, USA, caused a thin grass stem to pierce a thick wooden board; and a clover leaf actually penetrated a thick wooden board. Like a wedge, it was embedded deeply into the mud wall. However, the wind speed at the center of the tornado is very small or even calm, which is very similar to the situation in the eye of a typhoon.

What is especially scary is the low pressure inside the tornado. This low pressure can be as low as 400 mbar or even 200 mbar, while a standard atmospheric pressure is 1013 mbar. Therefore, where a tornado sweeps, it is like a special suction pump, often sucking up the water, sand, dust, trees, etc. it touches, forming a tall column. This is what people in the past called "dragon" Hanging upside down” or “dragon sucking water”. When a tornado rolls certain colored substances or other substances on land and fish in the sea to high altitudes, moves them to a certain place, and then falls to the ground with heavy rain, it forms "fish rain", "blood rain", "grain rain", etc. "Money rains".

When a tornado sweeps over the top of a building or vehicle, its internal air pressure is extremely low, causing a strong air pressure difference inside and outside the building or vehicle, causing the building or vehicle to collapse in an instant. explode". If the explosive effect of a tornado and the huge wind force exert their power at the same time, the damage and losses they cause will be extremely serious.

However, under normal circumstances, if a tornado passes through a residential area, bricks, broken wood and other debris will fly in the sky. Due to the high wind speed, it can also cause casualties to people and livestock, and destroy trees. and holes were smashed into telephone poles. Even small pebbles can pass through glass like bullets without shattering it.

According to statistics, tornadoes have occurred in every land country, and the United States is the country with the most tornadoes. Countries such as Canada, Mexico, the United Kingdom, Italy, Australia, New Zealand, Japan, and India also have many opportunities for tornadoes. Tornadoes in my country mainly occur in South China and East China, and they often appear on the Paracel Islands in the South China Sea.

Because the occurrence of tornadoes is closely related to the occurrence of severe thunderstorms, tornadoes generally appear in the warm season.

However, in the cold season when there are no thunderstorms, as long as there are strong convection conditions, tornadoes can also appear.

Tornadoes can occur during the day or night, but most occur in the afternoon. Sometimes, several tornadoes appear together at the same time.

Tornados may also be born from the smoke and water vapor produced by volcanic eruptions and large fires. This type of tornado is called a firespout or smokespout.

The range of various tornadoes is very small and their lifespan is very short, which brings great difficulties to scientific research and forecasting. However, before a tornado arrives, as long as you pay attention, there will always be some weather phenomena and characteristics worth noting. For example, before a tornado is generated, the atmosphere is very unstable, the cloud convection is strong, the air pressure is significantly reduced, the bottom of the cloud is particularly turbulent, etc. This is helpful for predicting tornadoes. In addition, weather radar plays an important role in detecting and tracking tornadoes. It can detect thunderclouds up to 300 kilometers away. Once a hook-shaped echo of a tornado is detected in the radar, an alert can be issued. However, when some tornadoes appear, this hook echo is not obvious. Therefore, it is often more reliable to use a combination of radar and visual inspection. When observers spot a tornado, they should immediately report it to the meteorological department, which can be tracked with radar. There will then be a certain amount of time to issue warnings to residents and units in the path of the tornado.

The emergence of weather satellites has added new detection tools to tornado forecasting, especially cloud photos taken by geostationary satellites, which play a more important role in monitoring the occurrence of tornadoes. Satellites can observe day and night and can see smaller targets.

If satellites and radars are combined, the changes in tornadoes can be continuously observed and warnings can be issued half an hour before the tornado occurs