How are typhoons formed?

Conditions for tropical depression or cloud disturbance to develop into typhoons. For example, (1) the sea surface water temperature is above 26-27°C, (2) the ambient air flow has strong cyclonic horizontal shear, (3) the shear between the upper and lower ambient air flows is much smaller, (4) low pressure or disturbance At least a few latitudes from the equator and so on. Since people do not fully understand the formation of typhoons, the above listed are only the necessary conditions for the formation of typhoons.

Generally speaking, for the occurrence of a typhoon, the following basic conditions need to be met:

1. First, there must be a sufficiently broad tropical ocean surface. This ocean surface requires not only the sea surface The temperature must be higher than 26.5°C, and in a layer of seawater 60 meters deep, the water temperature must exceed this value. The vast ocean surface is the necessary natural environment for the formation of typhoons. Because of the friction between air molecules inside the typhoon, an average of 3100-4000 calories/cm**2 of energy is consumed every day. This huge energy can only be released by the vast tropical ocean. Only latent heat can be supplied. In addition, the strong winds rotating around the tropical cyclone will cause the sea water near the center to churn. In the center of the typhoon where the air pressure drops very low, it can even cause the ocean surface to surge upward, and then spread out. As a result, the sea water moves from the center of the typhoon to the surrounding areas. tumbling. This churning phenomenon of sea water in typhoons can affect a depth of 60 meters. On the ocean surface where the sea water temperature is lower than 26.5°C, 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°C during this churning process, this warm water layer must be about 60 meters thick.

2. Before a typhoon forms, there must be a weak tropical vortex. We know that the operation of any machine consumes energy, which requires an energy source. A typhoon is also a "heat engine". It rotates at such a huge scale and speed and consumes a lot of energy, so it needs an energy source. The energy of typhoons comes from water vapor on tropical oceans. In a pre-existing tropical vortex, the air pressure in the vortex is lower than the surrounding air. The surrounding air carries a large amount of water vapor to the center of the vortex, and moves upward in the vortex area; the moist air rises and the water vapor condenses. Only by releasing huge latent heat of condensation can the big machine of typhoon operate. Therefore, even if there is a supply of water vapor from the tropical ocean with high temperature and humidity, it is impossible for a typhoon to form if there is no strong rise of air to cause condensation and release of latent heat. Therefore, the upward movement of air is an important factor in generating and maintaining typhoons. However, the necessary condition is the first existence of a weak tropical vortex.

3. There must be a large enough earth rotation deflection force. Because the geostrophic deflection force at the equator is zero and gradually increases toward the poles, the location of the typhoon is approximately 5 latitudes or more away from the equator. Due to the rotation of the earth, a force is generated that changes the direction of the air flow, which is called the "earth rotation deflection force". On a rotating Earth, the effect of the Earth's rotation makes it difficult for the surrounding air to flow directly into the low pressure. Instead, it rotates counterclockwise along the center of the low pressure (in the Northern Hemisphere).

4. Above weak low pressure, the difference in wind direction and speed between high and low altitudes is smaller. In this case, the upper and lower air columns act in unison, and heat easily accumulates in the upper air, causing warming. Once a cyclone is generated, the ambient airflow above the friction layer will flow along the isobars, and the upper-level warming effect can be further completed. In the area north of 20°N, climate conditions have changed, mainly due to strong upper-level winds, which is not conducive to warming, and typhoons are less likely to occur.

The above are only necessary conditions for the occurrence of typhoons. Meeting these conditions does not mean that a typhoon will occur. The occurrence of typhoons is a complex process that has not yet been fully understood.