Why is a typhoon called a "typhoon"?

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The formation and structure of typhoons

China Broadcasting Network 2006-05-17 20:34 :46

The structure of a typhoon

The scope of a typhoon is very large. Its diameter often ranges from hundreds of kilometers to thousands of kilometers, and its vertical thickness is more than ten kilometers. The ratio is about one to fifty.

Typhoons can generally be divided into three parts in the horizontal direction: the typhoon periphery, the typhoon body and the typhoon center. The periphery of a typhoon is a spiral cloud belt, usually 400-600 kilometers in diameter, sometimes up to 800-1000 kilometers; the typhoon body is a vortex area, also called a cloud wall area, which is composed of some tall convective clouds, with a diameter of generally 200 kilometers kilometers, sometimes up to 400 kilometers; from the typhoon center to the typhoon eye area, the diameter is generally 10-60 kilometers, the larger ones are more than 100 kilometers, the small ones are less than 10 kilometers, most of them are circular, some are oval or not. regular.

Typhoons are divided into three parts in the vertical direction: the inflow layer, the middle layer and the outflow layer. The inflow layer is from the sea surface to a height of 3 kilometers, the middle layer is from a height of about 3-8 kilometers, and the outflow layer is from a height of about 8 kilometers to the typhoon top. In the inflow layer, the surrounding air flows inward in a counterclockwise (in the northern hemisphere) direction. The closer to the center, the greater the wind speed, which brings a large amount of water vapor from outside the typhoon into the interior of the typhoon. The airflow in the middle layer mainly moves around the center, and the bottom inflow phenomenon reaches the clouds. The wall area basically stops, and then the airflow makes a spiral upward movement around the eye wall; when the rising airflow in the middle layer reaches the outflow layer, it spreads outward. Part of the outflow air mixes with the surrounding air and then sinks to the bottom layer, and part of it sinks in the eye area. It forms the vertical circulation area of ??the typhoon. The temperature of a typhoon becomes higher toward the center, and the pressure becomes lower toward the center.

The formation of typhoons

From the structure of typhoons, we can see that there must be unique conditions for the generation of such a huge behemoth. First, there must be a vast atmosphere of high temperature and high humidity. The temperature and humidity of the bottom atmosphere on the tropical ocean are mainly determined by the sea surface water temperature. Typhoons can only form on warm ocean surfaces where the sea temperature is higher than 26°C-27°C, and the seawater temperature within 60 meters is higher than 26°C. ℃ -27 ℃; secondly, there must be an initial disturbance in which the lower atmosphere converges towards the center and the upper atmosphere diffuses outward. Moreover, high-level divergence must exceed low-level convergence to maintain sufficient updraft and low-level disturbances to continue to strengthen. Third, the wind speed in the vertical direction cannot differ too much, and the relative movement of the upper and lower air is very small, so that the water vapor condensation released in the initial disturbance can be released. The latent heat energy is concentrated and stored in the air column in the typhoon eye area, forming and strengthening the typhoon warm center structure; fourth, there must be a large enough geostrophic deflection force, and the earth's rotation is conducive to the generation of cyclonic vortices. The geostrophic deflection force is close to zero near the equator and increases toward the north and south poles. Typhoons occur on the ocean surface about 5 latitudes or more from the equator.

Source: Hainan News Network Editor: Li Tingting