How did typhoons form in Guangdong and coastal areas?

There are often many weak tropical eddies on the surface of tropical oceans, which are called "embryos" of typhoons, because typhoons always develop from such weak tropical eddies. Through meteorological satellites, it is found that only about 10% of a large number of tropical eddies on the ocean surface can develop into typhoons. The occurrence of a typhoon requires the following basic conditions:

1. First of all, there must be a wide enough tropical ocean surface, which requires not only that the surface temperature of seawater is higher than 26.5℃, but also that the water temperature in a layer of seawater 60 meters deep should exceed this value. Among them, the vast ocean surface is the necessary natural environment for the formation of typhoons, because the friction between air molecules in typhoons consumes an average of 365,438+000-4,000 calories/cm **2 of energy every day, and this huge energy can only be supplied by the latent heat released by the vast tropical ocean. In addition, the strong wind around the tropical cyclone will make the sea water churn around the center, even in the typhoon center where the air pressure drops very low, and then spread around, so the sea water will churn around from the typhoon center. In a typhoon, this sea churning phenomenon can affect the depth of 60 meters. On the ocean surface where the seawater temperature is lower than 26.5℃, it is difficult to maintain a typhoon due to insufficient heat energy. In order to ensure that the sea surface temperature is always above 26.5℃ during this tumbling process, this warm water layer must have a thickness of about 60 meters.

2. There must be a weak tropical vortex before the typhoon is formed. We know that the operation of any machine consumes energy, which requires energy. Typhoon is also a "heat engine". It rotates there at such a huge scale and speed and consumes a lot of energy, so it needs an energy source. The typhoon's energy comes from the water vapor in the tropical ocean. In a pre-existing tropical vortex, the air pressure in the vortex is lower than that around it, and the air around it carries a lot of water vapor to the center of the vortex, causing upward movement in the vortex area; Wet air rises and water vapor condenses, releasing huge latent heat of condensation, which can make typhoons run. Therefore, even if there is a tropical ocean surface with high temperature and high humidity to supply water vapor, it is impossible to form a typhoon without the strong rise of air and the condensation and release of latent heat. Therefore, the upward movement of air is an important factor to produce and maintain typhoons. But the necessary condition is that a weak tropical vortex exists first.

3. There should be enough earth rotation deflection force. Because the geostrophic deflection at the equator is zero and gradually increases to the poles, the typhoon is located about 5 latitudes away from the equator. Due to the rotation of the earth, a force that changes the direction of air flow is generated, which is called "Earth rotation bias force". On the rotating earth, the rotation of the earth makes it difficult for the surrounding air to flow directly into the low pressure, but rotates counterclockwise along the center of the low pressure (in the northern hemisphere).

4. Above weak low pressure, there is little difference between high and low air direction and wind speed. In this case, the upper and lower air columns work together, and the high-altitude heat is easy to accumulate, thus heating up. Once the cyclone is generated, the ambient airflow above the friction layer will flow along the isobar, and the warming effect of the upper layer can be further completed. In the area north of 20 N, the climatic conditions have changed, mainly because the high-rise wind is very strong, which is not conducive to warming, and typhoons are not easy to appear.

These are just the necessary conditions for a typhoon. Having these conditions does not mean that there will be a typhoon. The occurrence of typhoon is a complicated process, which has not been fully understood so far.