Why is the typhoon center windless and sunny? The typhoon center is low pressure, shouldn't the airflow rise to form precipitation?

Typhoon is a powerful destructive cyclone vortex. It is a mature typhoon, and its bottom layer is divided into three areas according to the speed of convergent airflow: ① outer ring, also called windy area. From the edge of typhoon to the outer edge of vortex area, the radius is about 200 ~ 300 km, and its main feature is that the wind speed to the center increases sharply, and the wind power can reach more than 6 levels; ② The middle circle, also called vortex area. From the edge of the windy area to the eye wall of the typhoon, the radius is about 100km, which is the area with the strongest convection, wind and rain and the most destructive force in the typhoon. ③ Inner ring, also called eye area of typhoon. The radius is about 5 ~ 30km. Most of them are round, and the wind speed decreases rapidly or the wind is calm.

The horizontal distribution of various meteorological elements and weather phenomena in typhoon can be divided into three areas: outer cloud area (including outer cloud area and inner cloud area), cloud wall area and typhoon eye area. The vertical direction can be divided into three levels: low-altitude inflow layer (below about 1 km), high-altitude outflow layer (above about 10 km) and middle-level updraft layer (from about 1 km to 10 km) (Figure 1 typhoon structure diagram). In the lower layer around the typhoon, several spiral air currents with isobars in the typhoon area are involved in the typhoon area and converge to rise, which promotes the development of the convective cloud system and forms the outer and inner cloud areas of the typhoon. There are several spiral rain belts in the corresponding cloud system. The more spiral airflow involved in a typhoon, the faster the tangential wind speed becomes. At a certain distance from the typhoon center, the airflow no longer hovers, so a lot of wet air is forced to rise strongly, forming a towering cloud wall around the center. The top of the cumulonimbus cloud wall can be as high as 19 km, which is the cloud wall area.

In typhoon, the maximum wind speed occurs inside the cloud wall, and the maximum rainstorm occurs in the cloud wall area, so the cloud wall area is the storm area most prone to disasters. When the updraft in the cloud wall reaches high altitude, due to the weakening of the pressure gradient, a large amount of air is forcibly thrown out, forming an outer layer, while a small amount of air flows inward into the typhoon center and sinks, resulting in a clear typhoon center, namely the typhoon eye area. The radius of typhoon eye is about 10 ~ 70km, with an average of about 25km. The release and warming of latent heat in the cloud wall area and the sinking and warming of the typhoon eye area make the typhoon a warm-hearted low-pressure system.

At the lower level, typhoons mainly flow into low-pressure inflow. Because of the angular momentum balance, the inner region can produce strong wind speed, and the outflow airflow of anticyclone is in the upper layer. Strong upward movement connects the upper and lower circulation, which is the main feature of typhoon circulation. The hottest temperature in a typhoon is caused by the sinking movement, which occurs at the inner edge of the eye wall, where there is the strongest sinking movement. The convergence is strongest at the maximum wind speed radius in the lower layer of typhoon, and the maximum wind speed radius does not change much with height, and it is in the eye wall.

The air pressure near the typhoon center is low, but the typhoon eye is high. Because the air near the typhoon center is heated and rising, there is a vacancy below, so the space above the typhoon eye will fall in time to replenish, and the airflow will sink to form high pressure. The area controlled by high pressure is calm.