What is a typhoon? How is it formed? What are the characteristics? Major danger? How to prevent and rescue?

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, Japan and East Asia. It is called a whirlwind in the southern hemisphere.

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.

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 in which 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;

3. The difference of vertical wind speed should not be too big, and the relative motion of 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. Typhoons basically occur on the ocean surface about 5 latitudes from the equator.

Typhoon is a very destructive and disastrous weather system, but sometimes it can also play a beneficial role in eliminating drought. Its harmfulness mainly includes three aspects:

(1) Strong wind. 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 mm ~ 300 mm in the area it passes through, and a few typhoons can produce torrential rain above1000 mm. The rainstorm caused by typhoon 1975 in the upper reaches of Huaihe River created the extreme value of rainstorm in Chinese mainland and caused the "75.8" flood in Henan.

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

Strengthening the monitoring and forecasting of typhoons is an important measure to reduce typhoon disasters. Meteorological satellites are mainly used to detect typhoons. The existence and size of the typhoon can be clearly seen on the satellite cloud picture. Using meteorological satellite data, we can determine the location of typhoon center, estimate the intensity of typhoon, monitor the direction and speed of typhoon movement, and the area where severe storms occur, which plays a key role in preventing and mitigating typhoon disasters. When the typhoon reaches the offshore, the radar can also detect it. There are also forecasters of meteorological stations, who, based on all kinds of information obtained, analyze the trend of typhoons, the place and time of landing, issue typhoon forecasts, typhoon emergency reports or emergency warnings in time, serve the public through television, radio and other media, and provide decision-making basis for governments at all levels. Issuing typhoon forecast or emergency report is an important measure to reduce typhoon disaster.