What are the formation and characteristics of typhoons?

Typhoon (or hurricane) is a strong tropical cyclone produced on the surface of tropical ocean. It's just that the names vary from place to place. Tropical cyclones that occur in the Indian Ocean, the western North Pacific and the west of the international international date line, including the South China Sea, are called "typhoons"; Tropical cyclones in the Atlantic Ocean or the eastern North Pacific Ocean are called hurricanes. In other words, typhoons are called "hurricanes" in Europe and North America and "typhoons" in East and Southeast Asia. Known as "cyclone storm" in the Bay of Bengal; In the southern hemisphere, it is called "cyclone"

Schematic diagram of typhoon

Typhoons are often accompanied by strong winds and strong convective weather such as heavy rain or torrential rain. The wind rotates counterclockwise in the northern hemisphere (clockwise in the southern hemisphere). On the meteorological map, the isobar and isotherm of typhoon are approximately a set of concentric circles. The typhoon center is a low pressure center, which is dominated by the vertical movement of airflow. It was calm and sunny. Near the eye of the typhoon, there is a vortex wind and rain area with heavy wind and rain.

The typhoon with the strongest intensity and the lowest pressure near the center in history is the super typhoon Taibei (English: Typhoon Tip, translated by Taiwan Province Province: Dipu), 1979 caused extensive floods in Japan.

Formation of typhoon

The direct exposure of tropical sea surface to sunlight makes the temperature of sea water rise, and the sea water evaporates into steam to take off, while the cooler air around it flows in to replenish and then rises again. This cycle will eventually expand the whole airflow and form a "wind". Due to the vastness of the ocean, the diameter of air circulation is increasing, even thousands of meters. Due to the high-speed rotation of the earth from west to east, there is friction between the airflow column and the surface. The closer to the equator, the stronger the friction, which makes the steering column rotate counterclockwise (clockwise in the southern hemisphere). Because the speed of the earth's rotation is fast, the airflow column can't keep up with the speed of the earth's rotation, which forms the feeling of going west and forms the typhoon and typhoon path we are talking about now.

In tropical or subtropical oceans where the sea surface temperature exceeds 26℃, due to the high temperature near the ocean surface, a large amount of air expands and rises, which reduces the air pressure near the ocean surface, and the peripheral air continuously flows in and rises. Affected by the geostrophic force, the inflowing air rotates. The rising air expands and cools, and when the water vapor in it cools and condenses into water droplets, it will release heat and promote the rising of the lower air. In this way, the air pressure near the ocean surface drops lower, and the air rotates more violently, eventually forming a typhoon.

Such a huge behemoth must have unique conditions:

(1) should have a vast atmosphere with high temperature and humidity. The temperature and humidity of the bottom atmosphere on the tropical ocean surface are mainly determined by the sea surface temperature. Typhoons can only form on the warm ocean surface where the sea temperature is higher than 26~27℃, and the sea temperature within 60 meters is higher than 26~27℃.

(2) There should be an initial disturbance that the lower atmosphere converges to the center and the upper atmosphere spreads outward. Moreover, the divergence of the upper layer must exceed the convergence of the lower layer in order to maintain sufficient updraft and continuously strengthen the disturbance of the lower layer.

(3) The difference of vertical wind speed should not be too big, and the relative motion of upper and lower air is very small, so that the latent heat released by water vapor condensation in the initial disturbance can be concentrated in the air column in the typhoon eye area, forming and strengthening the typhoon warm center structure.

(4) If there is enough geostrophic deflection, the rotation of the earth is beneficial to the formation of cyclone vortex. The geostrophic deflection force is close to zero near the equator and increases at the north and south poles. Typhoons basically occur on the ocean surface about 5 latitudes from the equator.

The birthplace of typhoon

Typhoon sources are distributed in the vast low latitude ocean surface of the northwest Pacific Ocean. The tropical disturbance in the northwest Pacific intensified and developed to the initial position of typhoon, with a relatively concentrated zone in latitude and longitude. In the east-west direction, tropical disturbances developed into typhoons, which were relatively concentrated in four sea areas:

(1) China Nanhai; (2) East of Philippine Islands, Ryukyu Islands, Guam and other nearby waters (the most important birthplace of typhoons); (3) Sea area near Mariana Islands; ④ Sea area near Marshall Islands.

The disaster of typhoon

Disaster caused by typhoon

Typhoon is a disastrous weather system with strong destructive power. Its harmfulness mainly includes three aspects:

(1) gale. The maximum wind force near the typhoon center is generally above 8.

(2) heavy rain. Typhoon is one of the strongest rainstorm weather systems. Generally, it can produce rainfall of 150 ~ 300mm in the area it passes through, and a few typhoons can produce torrential rain above1000 mm.

(3) storm surge. Generally, typhoons will increase the water in coastal waters, and the maximum water increase in Jiangsu Province can reach 3 meters. Typhoon "9608" and "97 1 1" increased water, which made Jiangsu's coastal areas along the Yangtze River have a super-historical climax.

The benefits of typhoons

In China's coastal areas, typhoons hit us more or less every summer and autumn, causing great loss of life and property. As a kind of disastrous weather, it can be said that when it comes to typhoon, no one will show a good impression on it. However, everything has duality. Typhoon has brought disaster to human beings, but if there is no typhoon, human beings will be more miserable. Scientific research has found that typhoons have at least the following benefits for human beings:

(1) Tropical storms and typhoons have brought people abundant fresh water. Typhoon brings a lot of rainfall to the coast of China, the coast of the Sea of Japan, India, Southeast Asia and the southeastern United States, accounting for more than 1/4 of the total precipitation in these areas, which is of great significance to improving the fresh water supply and ecological environment in these areas.

(2) The tropical and subtropical areas near the equator have the longest sunshine time, and the dry heat is unbearable. If there is no typhoon to dissipate heat in these areas, it will be hotter there and the surface sand shortage will be more serious. At the same time, the cold zone will be colder and the temperate zone will disappear. There will be no spring city like Kunming in China, and there will be no evergreen Guangzhou. "Beidacang" and Inner Mongolia grassland will also cease to exist.

(3) The maximum speed of a typhoon can reach more than 200 kilometers per hour, and it will destroy everything it goes. This huge energy can directly cause disasters to mankind, but it also keeps the earth in thermal balance and makes mankind live and work in peace and contentment.

(4) Typhoons can also increase fishing. Every time a typhoon blows, it turns over the river, rolling up the nutrients in the river bottom and the sea, increasing the bait, attracting fish to gather near the water surface, and naturally increasing the catch.

About typhoon prevention (1), never go swimming in the sea. The typhoon came, the beach helped the tide, and the waves were extremely fierce. Swimming on the beach is dangerous, so don't go to the seaside.

(2) Don't save yourself blindly after being injured, please call 120. Emergency accidents such as trauma, fracture and electric shock are the most common in typhoons. Trauma is mainly head trauma, which is caused by fallen trees, telephone poles or falling objects such as flower pots and tiles. Electrical injuries are mainly caused by being hit by a blown wire or stepping on a wire covered under a tree. Don't walk barefoot, you'd better wear rain boots, which are waterproof and insulated to prevent electric shock. Watch carefully before you walk, so as not to step on the wire. Pay attention when passing through the alley, because accidents such as fence and telephone pole collapse are easy to happen. Pay attention to avoid falling objects from high buildings and downstairs. In case of emergency, dial 120 first. Don't move the wounded or find a car for first aid without authorization. Improper movements will cause more harm to patients with fractures, and in severe cases, paralysis will occur.

(3) As far away from the construction site as possible. It is best for residents to keep a little distance when passing through the construction site, because some construction site walls may loosen after rainwater infiltration; There are also some fences that may collapse; Some materials scattered on high buildings that are not collected in time, such as steel pipes and hammers, may be blown down by the wind; Where there are tower cranes, more attention should be paid to safety, because if the wind is strong, the tower crane arm may be broken. In some places, the facade of the building is being renovated. When people pass the scaffolding, they'd better go around and don't walk under it.

(4) Be sure to travel, and it is recommended to take the train. Among the three modes of transportation: aviation, railway and highway, highway traffic is generally most affected by typhoon. If you must travel, it is recommended not to drive by yourself, and it is best not to take a bus. You can choose to take the train.

(5) For the safety of yourself and others, please check the doors, windows and balconies at home. Before the typhoon comes, the balcony, flower pots outside the window and other items should be moved indoors. Don't go out at will, parents take care of their children. Resident users should bolt doors and windows, especially aluminum alloy doors and windows, to ensure safety. When traveling, please pay attention to stay away from windward doors and windows, avoid the rain and stay under big trees.