About temperate cyclones and tropical cyclones

The extratropical cyclone appears in the form of elliptical air vortex in the middle and high latitudes, which has the nature of cold center and is one of the important weather systems that affect large-scale weather changes. The average diameter of extratropical cyclones is 1000 km, ranging from several hundred km to over 3,000 km. The cyclone moves eastward with the airflow to the west of the upper air, with a warm front before and a cold front after, and the south side of the fluctuation at the junction of the two is a warm area. The whole life cycle of extratropical cyclones from generation, development to extinction is generally 2-6 days. Sometimes 2-5 extratropical cyclones are formed one after another on the same front, advancing from west to east in turn, which is called "cyclone family". Temperate cyclones have an important influence on the weather changes in middle and high latitudes. Rainy weather, sometimes accompanied by heavy rain or strong convective weather, sometimes the maximum wind force near the ground can reach more than 10.

Some extratropical cyclones are developed from waves on the front. Due to some reasons, waves are formed on the front, and a closed isobar appears near the peak of the waves, which gradually develops into a complete cyclone.

Temperate cyclones can also be transformed from tropical cyclones. When a tropical cyclone moves northward to the temperate zone, it loses its characteristics and becomes an temperate cyclone due to the influence of the westerly trough. On the other hand, depending on its location and intensity, the influence range of large-scale extratropical cyclones may exceed that of temperate regions, and even subtropical regions may be affected.

There used to be a stationary front on the ground, with cold air heading north and warm air heading south. Cold air moves from east to west, and warm air moves from west to east. When cold air is inserted southward under the front, warm air rises northward, and a closed isobar of 1 ~ 2 appears.

During this period, the extratropical cyclone can be shown in the visible satellite cloud image as the front cloud band widens, bulges to the cold region, turns white in color, and the middle and high clouds increase.

With the development of fluctuation, the air pressure drops further, the closed isobar increases, the cold air pushes further south, showers or snow showers appear near the cold front, and precipitation occurs before the warm front, and the precipitation area expands. With the development of cyclone, the disturbance at the lower level gradually develops to the upper level, the airflow spirals up, and the trough at the upper level gradually deepens.

During this period, the extratropical cyclone shows that the frontal cloud belt rises more obviously on the satellite cloud image, and the back boundary of the middle and high clouds begins to sag inward.

At the peak of cyclone development, it has become a circular closed cycle from the ground to a height of 500 mbar. The cold front on the ground gradually caught up with the warm front and lifted the warm air on the ground, and the cyclone began to stop. At this time, the range of clouds and rain is the largest, the intensity is strengthened, the wind is increased, and the weather changes the most dramatically. However, because the ground has been occupied by cold air and become a cold vortex, the cyclone began to weaken. During this period, the extratropical cyclone showed obvious dry tongue and obvious spiral structure at the back of the cloud system on the satellite cloud image. The cloud belt extends to the center of the vortex.

Generally, there are the following action routes. The most common path is to move to the northwest and land in Taiwan Province Province of China and the southeast coast. Move westward, cross the Philippines and enter the South China Sea of China; (3) Affected by subtropical high, front, easterly wind and other tropical cyclones nearby, various abnormal paths appear; Parabolic trajectory does not land in Chinese mainland, but passes through the East China Sea of China, moves to the Korean Peninsula and Japan, and finally degenerates into an extratropical cyclone.

The biggest feature of tropical cyclones is that their energy comes from the latent heat released when water vapor cools and solidifies. Other weather systems, such as extratropical cyclones, are mainly caused by the temperature difference on the cold northern horizontal plane. Tropical cyclones will weaken and dissipate or become temperate cyclones after landing or moving to the surface of the ocean with lower temperature because of losing the energy provided by warm and humid air.

The airflow of tropical cyclone rotates around the center under the action of Coriolis force. Tropical cyclones rotate counterclockwise in the northern hemisphere and clockwise in the southern hemisphere.

Different regions have different names for tropical cyclones. China, Taiwan Province Province, Japanese, Vietnamese, Philippine and other places along the western Pacific are used to calling local tropical cyclones typhoons. The Atlantic is used to calling local tropical cyclones hurricanes. Other places have different names for tropical cyclones. Known as "dynamic-dynamic" meteorology in Australia, only tropical cyclones with a certain wind speed will be named "typhoon" and "hurricane".

[Edit this section] Cyclone structure

Structure of Tropical Cyclone A mature tropical cyclone has the following parts:

▲ Ground low pressure

The center of tropical cyclone near the ground or sea surface is a low pressure area. The lowest pressure (870 hectopascals) recorded on the earth's sea level was recorded at the center of the typhoon tip, which is the strongest tropical cyclone ever recorded.

▲ Warm heart

The warm and humid air of tropical cyclone rotates and rises around the center. In this process, water vapor condenses and releases a lot of latent heat, and heat energy is distributed vertically near the center. The temperature inside the tropical cyclone is higher than that outside the cyclone at all heights (except near the sea surface).

▲ Central Miyun District

A dense cloud area around the center of a tropical cyclone, usually cirrus clouds produced by thunderstorms.

▲ Typhoon Eye

The circulation center of strong tropical cyclone is downdraft, which will form an eye. The weather in the eyes is usually calm, cloudless and even sunny in Wan Li (but the sea may still be rough). The eye of the wind is usually round, ranging from 2 km to 370 km in diameter. The eye of a weak tropical cyclone may be covered by the central dense cloud area, or even have no eye structure.

▲ Eye wall (or eye wall)

In a typhoon, the eye is surrounded by a barrel-shaped eye wall. Convection in the eye wall is very strong, and the height of its cloud is usually the highest among tropical cyclones, and the intensity of precipitation and wind is also the highest among tropical cyclones. Strong tropical cyclones have an eye wall replacement cycle, which produces a new outer eye wall to replace the inner wall. The reason is that the spiral rain belt around the eye wall of tropical cyclone gradually moves inward after recombination, stealing water and energy from the eye wall. At this stage, tropical cyclones enter a weakening process. At the periphery, the new eye wall completely replaces the old eye wall, and if the environment permits, the tropical cyclone will strengthen again. Through multi-frequency microwave scanning and radar, it can be clearly observed that tropical cyclones have binocular walls during the eye wall renewal period; If the eye wall replacement process of tropical cyclone is obvious, it can be observed from visible light and infrared satellite images.

▲ spiral rain belt

Spiral rain belt is a strong convective cloud and thunderstorm belt moving around the center of tropical cyclone. In the northern hemisphere, the spiral rain belt moves counterclockwise around the center. The spiral rain belt will bring storms, but it will be calmer between the two rain belts. Tornadoes sometimes form in tropical cyclones and spiral rain belts near land. Tropical cyclones with multiple spiral rain belts are generally strong and mature; But there are also some "wheel hurricanes", whose main feature is that there is no spiral rain belt.

▲ external circulation

All low-pressure systems need high-altitude divergence to continue to strengthen, and the divergence of tropical cyclones flows out from all directions. Due to the Coriolis force, the high altitude of tropical cyclone is an anticyclonic divergent circulation. The wind on the ground or sea surface rotates inward, weakens with the increase of height, and finally changes direction. This feature is related to the warm core structure in the center of tropical cyclone, so tropical cyclone needs weak vertical wind shear environment to maintain the warm core structure in order to continue divergence.

Tropical cyclone grade

Committee of Military Affairs

Use a two-minute average wind speed.

1. tropical depression, and the maximum average wind speed near the bottom center is10.8 ~17.1m/s, that is, the wind force is 6~7;

2. Tropical storm, the maximum average wind speed near the bottom center 17.2~24.4m/s, that is, the wind force is 8~9;

3. Strong tropical storm, the maximum average wind speed near the bottom center is 24.5~32.6m/s, that is, wind10 ~1;

4. Typhoon, the maximum average wind speed near the bottom center is 32.7~4 1.4m/s, which is12 ~13;

5. Strong typhoon, the maximum average wind speed near the bottom center is 4 1.5~50.9m/s, which is14 ~15;

Six, super typhoon, the maximum average wind speed near the bottom center is ≥5 1.0m/s, that is, 16 or more.

Note: In fact, in order to prevent chaos, central weather bureau has never reported a typhoon with a wind force greater than 65m/s.

National Oceanic and Atmospheric Administration (USA)

Use the one-minute average wind speed.

Tropical depression) ≤33KT.

Tropical storm (34kt-63kt)

Typhoon category 1: 64 ~ 82 knots

Typhoon category 2 (83 ~ 95 knots)

Typhoon No.3 (96 ~ 1 13 kt)

Typhoon of magnitude 4 (1 14 ~ 135kt)

Typhoon category 5 > 135kt

Note: KT is the abbreviation of speed unit "knot", and the conversion ratio is1kt = 0.5144m/s.

JMA

Ten-minute average wind speed is adopted, which is the standard of the World Meteorological Organization.

Tropical depression (thermal depression) ≤33 knots

Typhoon (typhoon) 34KT~63 KT

Strong (strong) 64 ~ 84 kt

Very strong (very strong) 85 ~ 104kt

Violence (rampage) ≥ 105kt

Note: Typhoons are numbered internationally according to the ten-minute average wind speed (namely JMA standard).

Generation condition

The energy of tropical cyclones comes from the latent heat released by the condensation of water vapor. The formation conditions of tropical cyclones are still under study and have not been fully understood. It is generally believed that the generation of tropical cyclones must meet six conditions, but tropical cyclones may also be generated when these six conditions are not fully met.

The surface temperature of seawater is not lower than 26.5℃ and the water depth is not lower than 50m. The seawater at this temperature makes the upper atmosphere unstable enough to maintain convection and thunderstorms.

The temperature drops rapidly with height. This releases latent heat, which is the energy source of tropical cyclones.

Humid air, especially in the lower troposphere. Humidity in the atmosphere contributes to the formation of weather disturbances.

It needs to be generated in the area above five latitudes from the equator, otherwise the strength of Coriolis force is not enough to deflect and rotate the wind blowing to the low pressure center, and the circulation center cannot be formed.

The vertical wind shear becomes weak. If the vertical wind shear is too strong, the development of tropical cyclone convection will be hindered and its positive feedback mechanism will not start.

Pre-existing weather disturbance with circulation and low pressure center.

Generated location

Most tropical cyclones are formed in intertropical convergence zone, and intertropical convergence zone is an active area of thunderstorm activity in tropical regions around the world.

Tropical cyclones are generated in areas with high seawater temperature, usually above 27℃. They originated in the eastern part of the ocean, moved westward, and strengthened in the process of moving. Most of these systems are formed between north and south latitudes 10 and 30 degrees, and 87% are formed within 20 degrees. Because the Coriolis force gives and maintains the rotation of tropical cyclones, tropical cyclones are rarely generated within five degrees north and south latitude where the Coriolis force is the weakest. [20] However, tropical cyclones may also form in this area, such as 200 1 Typhoon Thrushcross, and tropical cyclone fire in 2004.

sports

Steering flow/current

The path of tropical cyclone is mainly influenced by large-scale turning current, and the movement of tropical cyclone is described by Dr. Neil Frank, former director of the National Hurricane Center of the United States, as "the leaves are pushed by the current".

Tropical cyclones around 20 degrees north and south latitude are mainly guided by the turning airflow of subtropical high (a high pressure area maintained in the ocean for many years) and move westward, so the airflow from east to west is called trade winds. In the North Atlantic and Northeast Pacific, tropical fluctuations will be guided by the trade winds from the west coast of Africa to the Caribbean and North America, and finally reach the central Pacific until the turning airflow weakens. These fluctuations (called easterly waves) are the precursors of many tropical cyclones in this area. In the Indian Ocean and the Western Pacific Ocean, the formation of storms is mainly influenced by the seasonal changes of intertropical convergence zone and monsoon trough, and the proportion of easterly waves forming tropical cyclones is smaller than that of the Atlantic Ocean and the Northeast Pacific Ocean.

Coriolis force is a phenomenon that inertial system moves on non-inertial system. Coriolis force does not really exist, but for an observer in a non-inertial system, he will think that the path of the inertial system is deviated, so he imagines an acceleration, which is multiplied by the mass of the object to become a virtual force. Although only the earth's rotation can produce Coriolis force, considering the shape of the earth's sphere, a latitude-related coefficient should be added. So the Coriolis acceleration on the earth is: where V is the horizontal component of the earth's rotation speed. Therefore, the higher the latitude, the greater the Coriolis acceleration and the zero Coriolis force at the equator. A special case of Coriolis force on the earth is called geostrophic deflection force, which has two main effects on cyclone motion. On the one hand, it determines the rotation mode of the cyclone system; On the other hand, it determines the direction of the cyclone. When air enters the low pressure center along the pressure gradient, the atmospheric flow will deviate to some extent due to the difference between the atmospheric flow and the earth's rotation mode. In the northern hemisphere, when the air north of the low pressure center moves south, it will deviate in the opposite direction to the earth's rotation; When the air moving south moves north, it will deviate from the direction of the earth's rotation, while the air in the southern hemisphere will deviate from the opposite direction. Because the Coriolis force is perpendicular to the speed of air to the center of low pressure, the power of cyclone system rotation is generated: the cyclone in the northern hemisphere rotates counterclockwise and the cyclone in the southern hemisphere rotates clockwise. Coriolis force also makes the cyclone system move to the poles, without strong influence of turning airflow. The part of tropical cyclone rotating to the poles will increase slightly due to Coriolis force, and the part rotating to the equator will increase slightly to the equator. The closer the earth is to the equator, the weaker the Coriolis force is, so the influence of Coriolis force on tropical cyclones is greater on the poles than on the equator. Therefore, tropical cyclones in the northern hemisphere will generally move northward, while tropical cyclones in the southern hemisphere will move southward when there is no other turning flow to offset the Coriolis force.

Although the Coriolis force determines the direction of cyclone rotation, the main driving force of its high-speed rotation is not the Coriolis force, but the result of conservation of angular momentum: air is pumped into the low-pressure center from the area far away from the cyclone range, and the angular momentum remains unchanged due to the increase of mass, which leads to a great increase in the angular velocity of cyclone rotation.

The most obvious movement of tropical cyclone cloud system is towards the center, and the principle of conservation of angular momentum also makes the inflow of air accelerate gradually when it approaches the center of low pressure. When the airflow reaches the center, it will start to flow upward and outward, so the upper cloud system will also flow outward. This is because the air that releases moisture is discharged from the high-altitude "chimney" of tropical cyclones. Divergence causes thin cirrus clouds to form at high altitude and rotate outside tropical cyclones, which may be the first warning signal of tropical cyclones.

Besides the rotation of tropical cyclone itself, the conservation of angular momentum also affects the moving path of cyclone. At low latitudes, the earth's rotation radius is large, so the airflow deviation is small; At high latitudes, the earth's rotation radius is small, so the airflow deviation is large. This force is also one of the reasons why tropical cyclones move northward in the northern hemisphere and southward in the southern hemisphere.

Interaction with mid-latitude westerlies

During 1973, Fujiwara effect occurred between Hurricane Ione and Hurricane Kirsten. When the tropical cyclone moves to higher latitudes, its path around the subtropical high will be changed by the low pressure area located at high latitudes. When the tropical cyclone moves to the poles and approaches the low pressure area, the easterly vector will gradually appear, which is the process of tropical cyclone turning. For example, a typhoon moving westward to the Asian continent may gradually turn to the north because of the low pressure area over China or Siberia, and then accelerate to the northeast and pass the Japanese coast. The typhoon turned to the northeast, because when it was located at the northern edge of the subtropical high, the turning airflow was from west to east.

Fujiwara effect

Fujiwara effect, or bistatic effect, refers to the state of interaction between two or more cyclones that are not far apart.

It often causes heat until the distance between them is so great that the Fujiwara effect disappears, or until they merge. If the intensity of two tropical cyclones is similar, they will rotate around the connection center between them until the influence of other weather systems or one of them weakens.

get off a ship

The official definition of "landing" is that the center of the storm passes through the coastline, but there will be storms in coastal and inland areas a few hours before the tropical gas lands. Because the strongest position of tropical cyclone wind is not in the center, even if tropical cyclone does not land, it may feel its strongest wind on land.

Mississippi, USA after Hurricane Katrina. The power released by mature tropical cyclones can reach 6x 10 14 watts, and tropical cyclones at sea cause huge waves and storms. Sometimes shipwrecks will be caused, which will affect international shipping. However, tropical cyclones cause the most damage when landing, and the main direct damage includes the following three points:

Gale: Hurricane-level winds are enough to damage or even destroy buildings, bridges and vehicles on land. Especially in areas where buildings are not reinforced, the damage is even greater. Strong winds also blow debris into the air, making the outdoor environment very dangerous.

Storm surge: The rising water level caused by the wind and air pressure of tropical cyclones can flood coastal areas, and it is even more harmful if it is suitable for astronomical climax. Among all kinds of losses caused by tropical cyclones, storm surge is often the most deadly.

Heavy rain: Tropical cyclones can cause continuous heavy rain. Heavy rain in mountainous areas may cause river flooding, mudslides and landslides.

Tropical cyclones also caused some indirect damage to the landing site, including:

Disease: stagnant water and damaged sewers after tropical cyclones may cause epidemics.

Damage to infrastructure system: Tropical cyclones may damage roads and power transmission facilities. And hinder the rescue work.

Agriculture: Wind and rain may destroy fish and agricultural products, leading to food shortage.

Salt wind: The salt in seawater is brought to the land with the huge waves caused by tropical cyclones, which will cause crops to wither when attached to the leaves of crops, and may cause electricity leakage when attached to cables.

The loss of life caused by tropical cyclones is immeasurable, but tropical cyclones will also bring important rainfall to arid areas. An important part of the annual rainfall in many areas comes from tropical cyclones. For example, tropical cyclones in the northeast Pacific bring rain to arid Mexico and the southwestern United States; Even nearly half of the annual rainfall in Japan comes from tropical cyclones.

Tropical cyclones are also an important mechanism for maintaining global heat and momentum balance. Tropical cyclones project the sun into tropical areas and convert it into seawater heat energy, which is brought to the mid-latitude and polar regions. Tropical cyclone is also a strong vortex disturbance, which transports the easterly angular momentum accumulated at the equator to the westerly belt in the mid-latitude region.

▲ observation

Observing strong tropical cyclones has always been a great challenge for human beings. Because they are mainly active in the ocean, most weather stations located on land cannot provide measurement data, and observation on the ground is generally only possible when tropical cyclones pass through islands or coastal areas. However, even if there is a tropical cyclone near the weather station, the weather station can generally only provide real-time data on the periphery of the storm, because if the strong storm is too close, the monitoring facilities of the weather station will be destroyed by strong winds.

Reconnaissance planes equipped with meteorological monitoring equipment will also be sent to the tropical cyclone center to extract measurement data. In the Atlantic Ocean, when tropical cyclones appear, the U.S. government will regularly send reconnaissance planes to monitor them. These reconnaissance planes are equipped with direct and remote sensing equipment to take readings, as well as airdrop equipment to measure wind speed, pressure, temperature and humidity at high altitude and sea level.

In 2005, an unmanned reconnaissance plane was sent to monitor tropical storm O 'Filja. Unmanned reconnaissance aircraft can fly to a lower altitude to monitor storms without worrying about the safety of pilots.

Annual average error of numerical model of Atlantic tropical storms and hurricanes by National Hurricane Center of the United States: The numerical forecast error of tropical cyclone path has been decreasing since1970s, and there is no reconnaissance plane monitoring storms in other parts of the world. The path of marine tropical cyclones is mainly tracked by visible and infrared satellite cloud pictures taken by meteorological satellites, and updated every half hour or quarter of an hour. Dvorak analysis is used to evaluate the intensity from the cloud image. When the storm approaches the coastal area, the Doppler radar echo image updated every minute on land plays an important role in locating tropical cyclones.

: stands for tropical cyclone warning center

Climatic survey of tropical cyclones along the coast of China

Tropical cyclone is also one of the major disastrous weather systems affecting China. During its activities, it is accompanied by strong winds, heavy rains, huge waves and storm surges. Therefore, although tropical cyclones can alleviate the summer drought in the passing areas, they will also cause great losses to people's lives and property. China coastal areas from Liaoning in the north to Guangdong and Guangxi in the south are likely to be attacked by tropical cyclones every year, with the largest number of tropical cyclones landing in Guangdong, Fujian and Taiwan Province provinces.

[Edit this paragraph] Idiom:

Different regions have different names for tropical cyclones. Taiwan Province Province, China, South Korea, Japan, Vietnam and the Philippines along the Pacific Northwest are used to calling local tropical cyclones typhoons. The coastal areas of the Atlantic Ocean and the Northeast Pacific Ocean are used to calling local tropical cyclones tropical depression, tropical storm or hurricane according to their intensity. In the southern hemisphere and the northern Indian Ocean, the word "cyclone" is used as the abbreviation of "tropical cyclone". Occurred in the Bay of Bengal and the Arabian Sea, known as cyclone storm; Near the Philippines, it is called "Bagua Palm" or "Baguio Wind"; Appearing in the South Indian Ocean and the northern coast of Australia, it is called "power", which means scheming, cunning and terrible, repeating "power" and telling people to be vigilant; What happened in the Indian Ocean east of Madagascar is called Mauritius. Meteorology, only tropical cyclones with a certain wind speed will be named "typhoon" or "hurricane".

Major source areas

1985 track map of all tropical cyclones in 2005. The North Pacific Ocean west of international date line produces the most tropical cyclones. There is almost no tropical cyclone activity in the South Atlantic. Almost all tropical cyclones are generated within 30 latitudes north and south of the equator. About 87% of them are within 20 degrees north and south latitude. Because of the weak geostrophic offset, there are few opportunities to form tropical cyclones within north and south latitudes 10 degrees, but it is not uncommon.

Every year, there are 80 tropical cyclones on average on the earth. The main producing areas are:

Northwest Pacific

Including the South China Sea, and the affected areas include China; The Philippines, South Korea, Japan, Vietnam and islands in the Pacific occasionally affect Thailand and Indonesia. Every year, tropical cyclones generated in the northwest Pacific Ocean account for one-third of the world. The coast of China is the place where tropical cyclones land the most in the world. Six to seven tropical cyclones land in the Philippines every year.

Eastern North Pacific

The second largest tropical cyclone producing area includes Mexico, Hawaii, Pacific island countries and, in rare cases, Baja California and northern Central America.

North Atlantic

Including the Caribbean and the Gulf of Mexico. The number of generations varies greatly each year, ranging from one generation to twenty generations, with an average of about ten generations per year. It mainly affects the States along the east coast of the United States and the Gulf Coast, Mexico and Caribbean countries, and occasionally affects Venezuela and Canada. In 2005, Hurricane Vince landed in Spain with the intensity of tropical depression, which was the only Atlantic storm that landed in Europe on record.

Southwest Pacific

It mainly affects Australia and Oceania countries.

north indian ocean

Including the Bay of Bengal and the Arabian Sea, mainly produced in the Bay of Bengal. There are two peaks in the North Indian Ocean monsoon season: one is April and May before the start of the monsoon, and the other is 65438+ 10 and 165438+ 10 after the end of the monsoon. It affects countries such as India, Bangladesh, Sri Lanka, Thailand, Myanmar and Pakistan, and sometimes the Arabian Peninsula.

Eastern South Indian Ocean

Affecting Indonesia and Western Australia.

Southwest Indian Ocean

It mainly affects Madagascar, Mozambique, Mauritius, reunion island, Tanzania, Comoros and Kenya. [54]

Rare resources

south atlantic

Due to the low seawater temperature and strong vertical wind shear, only three tropical cyclones were found in the South Atlantic, including tropical cyclone Katarina, which hit Brazil.

Southeast Pacific

Due to strong vertical wind shear, no tropical cyclone has been found in this area so far.

the Mediterranean Sea

Only a few storms like tropical cyclones have ever formed.

High latitude area

The water temperature is low and the vertical wind is strong for a long time, so it is difficult to generate tropical cyclones.

Very close to the equator.

The geostrophic deflection force in equatorial region is small, so it is difficult to form the rotating power of tropical cyclone. For example, Typhoon Thrushcross affecting Singapore at 200 1 and tropical cyclone Agni generated in the North Indian Ocean in 2004 are rare near-equatorial typhoons. The latitude of the Thrushcross generation is located at 1.5 degrees north latitude, and Agni is a record-breaking latitude of 0.7 degrees north latitude. The formation of Agni is a mystery, which needs scientists to explore.

generation time

Tropical cyclones are mainly generated in late summer, because the temperature of seawater is the highest at this time. But in the exact formation time, each sea area has its own unique seasonal changes. Globally, September is the most active month of tropical cyclones, while May is the least active month.

grading

The intensity of tropical cyclones is generally evaluated according to the average wind speed, and the World Meteorological Organization recommends using the ten-minute average wind speed. However, the National Hurricane Center, the Joint Typhoon Warning Center and the China Meteorological Bureau use one-minute and two-minute average wind speeds to calculate the sustained wind power of tropical cyclone centers. According to the definition of the United States and China, the average wind speed will be slightly higher than that of the United Nations. The approximate conversion formula of one-minute and ten-minute average wind speed is: ten-minute average wind speed = one-minute average wind speed multiplied by 0.88.

Different regions have different classification methods for tropical cyclones. In the United States, hurricanes are divided into one to five grades according to the saffir-simpson hurricane scale [62], and Australia has a similar method. The following is the classification of tropical cyclones with different intensities by district officials (referring to the Regional Specialized Meteorological Center (RSMC) or the Tropical Cyclone Warning Center (TCWC), except the Joint Typhoon Warning Center):

Classification of tropical cyclones (all converted into ten-minute average wind speed)

Ten-minute mean wind speed (knots) of Beaufort scale in the North Indian Ocean

0–6 & lt； 28 low pressure tropical disturbance tropical low pressure tropical low pressure tropical low pressure tropical low pressure tropical low pressure tropical low pressure tropical low pressure.

7 28-29 deep depression tropical depression

30-33 Tropical Storm

8–9 34–47 Cyclone Storm Moderate Tropical Storm Tropical Cyclone (Class I) Tropical Cyclone Tropical Storm

10 48–55 strong cyclone storm strong tropical storm tropical cyclone (level 2) strong tropical storm

1156–63 typhoons and hurricanes (level 1)

12 64–72 Extra strong cyclone storm tropical cyclone strong tropical cyclone (level 3) typhoon

Hurricane 73-85 (Level 2)

86-89 strong tropical cyclone (level 4) strong hurricane (level 3)

90-99 strong tropical cyclone

100–106 severe hurricane (level 4)

107- 1 14 strong tropical cyclone (level 5)

115–119 super tropical cyclone super typhoon

& gt 120 super cyclone storm and strong hurricane (level 5)

According to the notice of National Standard for Tropical Cyclone Grades issued by China Meteorological Bureau, tropical cyclones are divided into six grades according to the maximum wind speed near the bottom center, and "Typhoon" is only one of them.

1. Tropical depression. The maximum average wind speed near the bottom center 10.8- 17. 1 m/s, that is, the wind force is 6-7;

2. Tropical storm, the maximum average wind speed near the bottom center 17.2-24.4m/s, that is, the wind force is 8-9;

3. Strong tropical storm, the maximum average wind speed near the bottom center is 24.5-32.6m/s, that is, wind10-1;

4. Typhoon, the maximum average wind speed near the bottom center is 32.7-4 1.4m/s, that is,12-13;

5. Strong typhoon, the maximum average wind speed near the bottom center is 4 1.5-50.9 m/s, that is,14-15;

Six, super typhoon, the maximum average wind speed near the bottom center is ≥5 1.0 m/s, that is, 16 or more.

Models of tropical cyclones at all levels

The following are examples of tropical cyclones at all levels. Note that the following description is only for the storm in the cloud image, and other tropical cyclones of the same level may not have these characteristics. Tropical cyclones above typhoon (hurricane) level use saffir-simpson hurricane scale, so take all hurricanes in Atlantic Ocean or Northeast Pacific Ocean as an example.

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