Why is the wind direction of typhoon counterclockwise?

Typhoons and hurricanes are both strong tropical cyclones generated on the surface of tropical oceans, but they are called differently. Tropical cyclones that occur in the western part of the North Pacific Ocean and 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, which means hurricanes in the United States and typhoons in the Philippines, China and Japan.

Typhoons are often accompanied by strong winds and heavy rains. The wind rotates counterclockwise. Isobars and isotherms are approximately a set of concentric circles. The central air pressure is the lowest and the temperature is the highest.

Typhoon classification

Super typhoon: the maximum average wind speed near the center of the ground layer is ≥ 5 1.0m/s, that is, 16 or more.

Strong typhoon (STY): The maximum average wind speed near the bottom center is 41.5-50.9m/s, which is 14- 15.

Typhoon (TY): the maximum average wind speed near the center of the ground floor is 32.7-4 1.4m/s, which is 12- 13.

Severe tropical storm (STS): the maximum average wind speed near the bottom center is 24.5-32.6m/s, that is, wind10-1.

Tropical storm (TS): the maximum average wind speed near the bottom center 17.2-24.4m/s, that is, the wind force is 8-9.

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

typhoon track

The direction and speed of typhoon movement depend on the force acting on the typhoon. Power is divided into internal force and external force. The internal force is the resultant force from north to west caused by the different geostrophic skewness caused by the latitude difference between north and south within the typhoon range. The larger the typhoon range, the stronger the wind speed and the greater the internal force. The external force is the force of the external environment flow field on the typhoon vortex, that is, the guiding force of the easterly belt of the basic airflow on the south side of the subtropical high in the northern hemisphere. Internal force mainly plays a role in the initial generation of typhoon, while external force is the leading force to manipulate the movement of typhoon, so typhoon basically moves from east to west. Due to the influence of the shape, position and intensity of subtropical high, the typhoon's moving path is not uniform and becomes diverse. Take the typhoon moving path in the western North Pacific as an example, there are generally three moving paths.

(1) The westward typhoon moved from the east of the Philippines to the west, crossed the South China Sea, and finally landed on Hainan Island in China or northern Vietnam.

(2) Landing type: The typhoon moved to the northwest, crossed the Taiwan Province Strait, landed in the coastal areas of Guangdong, Fujian and Zhejiang, and gradually weakened into a low pressure. This typhoon has the greatest impact on China. The two typhoons "90 15" and "97 1 1" which have had the greatest impact on Jiangsu in recent years belong to this type.

(3) Parabolic type: The typhoon moves to the northwest first, then turns to the northeast when approaching the eastern coast of China, and turns to the vicinity of Japan, with a parabolic path.

After the typhoon is formed, it will generally move out of the source and experience the evolution process of development, weakening and extinction. A mature typhoon has a circular vortex radius of 5 OOKM ~ 1000 km and a height of 15 km ~ 20 km. Typhoon consists of three parts: peripheral area, maximum wind speed area and typhoon eye. The wind speed in the peripheral area increases from outside to inside, with spiral clouds and precipitation; The strongest precipitation occurs in the maximum wind speed area, with an average width of 8 km ~ 19 km, and there is a circular cloud wall between it and the typhoon eye; The typhoon eye is located in the center of the typhoon. The most common typhoon eye is round or oval, ranging in diameter from 10 km to 70 km, with an average of about 45km. The weather in typhoon eye is calm, partly cloudy, dry and warm.

Number of typhoons

China numbered the tropical depressions that entered the west of l50 degrees east longitude and the north of l0 degrees north latitude, and the maximum wind force near the center was 8, according to the sequence of occurrence every year. This is the "Typhoon X this year (tropical storm, strong tropical storm)" that we heard or saw on radio and television.

The number of typhoons is also the number of tropical cyclones. People want to number tropical cyclones, on the one hand, because a tropical cyclone often lasts for more than a week, and several tropical cyclones may appear in the ocean at the same time. With the serial number, there will be no confusion; On the other hand, the naming, definition, classification method and determination of the center position of tropical cyclones are different in different countries and methods, even in the same country, they are not exactly the same among different meteorological stations, which often leads to various misunderstandings and confusion in use.

Starting from 1959, China began to number the tropical cyclones (tropical storms and above) that occur or enter the Pacific Ocean and South China Sea north of the equator and west of 180 degrees east longitude every year according to the sequence of their occurrence. Offshore tropical cyclone. In the case of clear cloud structure and circulation, as long as the maximum average wind force near the center is above 7, it is also numbered. The serial number consists of four digits. The first two digits represent the year. The last two digits are the serial numbers of tropical cyclones above storm level in that year. For example, in 2003, Typhoon Du Fu 13, its serial number was O3 13. , representing the tropical cyclone with storm level 13 or above that occurred in 2003. Tropical depression and tropical disturbance are not numbered.