Information about typhoons

Typhoon is a strong tropical cyclone. Like the vortex in water, it is an air vortex that rotates rapidly around its center on the surface of tropical ocean and moves forward at the same time. Just like a gyro in motion, people sometimes compare it to an "air gyro". Because typhoons are often accompanied by violent storms, they are given a name different from ordinary strong winds in meteorology-typhoon.

Structure of typhoon

A typhoon covers a large area, often ranging from a few hundred kilometers to several thousand kilometers in diameter, with a vertical thickness of more than ten kilometers, and the ratio of vertical and horizontal areas is about one to fifty.

Generally speaking, a typhoon can be divided into three parts in the horizontal direction: typhoon periphery, typhoon main body and typhoon center. The periphery of the typhoon is a spiral cloud belt, generally 400-600 km in diameter, and sometimes it can reach 800-1000 km; Typhoon itself is a vortex area, also called cloud wall area, which is composed of some tall convective clouds, with a diameter of 200 kilometers in general and sometimes up to 400 kilometers. From the center of the typhoon to the eye of the typhoon, its diameter is generally 10-60 km, with the largest exceeding 100 km and the smallest less than 10 km. Most of them are round, oval or irregular.

Typhoon is vertically divided into inflow layer, middle layer and outflow layer. The inflow layer is from the sea surface to the height of 3 km, and the outflow layer is from the height of 3-8 km to the middle layer and from the height of 8 km to the typhoon top. In the inflow layer, the surrounding air flows counterclockwise (in the northern hemisphere), and the closer to the center, the greater the wind speed, and a large amount of water vapor is imported into the typhoon from the outside; The airflow in the middle layer mainly moves around the center, and the inflow phenomenon in the bottom layer basically stops when it reaches the cloud wall area, and then the airflow hovers around the eye wall; When the updraft in the middle layer reaches the outflow layer, it diffuses outward. Part of the outflow air sinks to the bottom after mixing with the surrounding air, and part sinks to the eye area, which constitutes the vertical circulation area of the typhoon. The higher the typhoon center temperature, the lower the center pressure.

Formation of typhoon

Judging from the typhoon structure, such a behemoth must have unique conditions. First of all, there must be a vast atmosphere with high temperature and high humidity. The temperature and humidity of the bottom atmosphere on the tropical ocean surface are mainly determined by the sea surface temperature, and typhoons can only form on the warm ocean surface where the sea surface temperature is higher than 26℃-27℃ and the sea surface temperature is higher than 26℃-27℃ within 60 meters. Second, 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 enough updraft and continuously strengthen the disturbance of the lower layer; Third, the vertical wind speed cannot be too different, and the relative motion between the upper and lower air is very small, so that the latent heat released by water vapor condensation in the initial disturbance can be stored in the air column in the typhoon eye area, forming and strengthening the typhoon warm center structure; Fourth, there must be enough geostrophic deflection, and the earth's rotation is conducive to the formation of cyclonic vortices. The geostrophic deflection force is close to zero near the equator and increases at the north and south poles. The typhoon occurred on the ocean surface about 5 latitudes from the equator.

Distribution of typhoons

There are certain conditions for the formation of typhoons. Therefore, its origin is also in a specific area. Typhoon is a "specialty" in tropical oceans. It often occurs on the tropical ocean surface of 5-25 degrees north and south latitude.

Typhoons in the northern hemisphere mainly occur from July to 10. Other seasons are obviously reduced. After the typhoon is formed, it has a certain moving path. Take typhoons in the northwest Pacific as an example: in winter and spring (June 1 1 to May of the following year), typhoons mainly turn north on the sea east of eastbound 130, enter the south-central South China Sea or land in southern Vietnam south of north latitude 16, and a few typhoons land in eastbound120-. In the midsummer season from July to September, the typhoon path further deviates to the northwest, and the coastal provinces of China from Guangxi to Liaoning may be hit by typhoons in this season; During the transition season from June to June in 10, typhoons mainly turn north on the sea east of 125, and the westbound path is relatively north, between 15-20, and a few can land in Guangdong, Taiwan Province, Fujian, Zhejiang and other places.

In addition to counterclockwise rotation (in the northern hemisphere), typhoon movement is mainly guided by large-scale weather systems such as subtropical high and long wave trough. Under normal circumstances, the typhoon moves smoothly. However, there are also a few typhoons with tortuous paths, such as stagnation, gyration, sharp turn, sudden change of moving speed and uncertain path.

The harm of typhoon

Typhoon has brought abundant rain to vast areas and become a rainfall system closely related to human life and production. However, typhoons always bring all kinds of injuries. Because of its sudden and destructive power, it is one of the most serious natural disasters in the world.

The destructive power of typhoons is mainly caused by strong winds, heavy rains and storm surges.

1. Strong typhoon is a huge energy pool, and its wind speed is above 17m/s, even above 60m/s ... According to the measurement, when the wind reaches 12, the wind pressure per square meter on the plane perpendicular to the wind direction can reach 230kg.

2. Rainstorm typhoon is a strong precipitation system. When the typhoon lands, the rainstorm center can drop 100-300mm a day, or even reach 500-800mm. The floods caused by typhoons and rainstorms are the most dangerous disasters. Typhoon rainstorm is strong, flood occurs frequently, spreads widely, and is fierce and destructive.

3. Storm Surge The so-called storm surge means that when the typhoon moves to the land, due to the typhoon's strong wind and low air pressure, the sea water accumulates strongly in the direction of the coast, the tide level rises sharply, and water waves are overwhelming to the coast. The storm surge of a strong typhoon can raise the coastal water level by 5-6 meters. Storm surge meets astronomical high tide level, resulting in high-frequency tide level, which leads to tidal overflow, seawall burst, washed away houses and various building facilities, flooded towns and farmland, and caused a large number of casualties and property losses. Storm surge will also cause coastal erosion and land salinization caused by seawater intrusion.