1, atmospheric humidity
When a typhoon passes through the ocean, it will bring a lot of water vapor. When the water vapor meets the updraft in the low pressure area of the typhoon center, the air begins to cool, and the water vapor condenses into clouds, resulting in large-scale rainfall.
2. The specific humidity increases
The low pressure area formed by typhoon will increase the specific humidity of the surrounding air. Specific humidity is the ratio of water vapor content to water vapor saturation in the air. When the specific humidity increases to a certain extent, the water vapor in the air will condense into water droplets and form rainfall.
3. Convective motion
The strong wind force brought by typhoon will cause convective movement. Through convection, the air will rise and cool, forming clouds, and the water droplets in the clouds will gradually increase, eventually forming rainfall.
Introduction to the formation process of typhoon;
Typhoons are all developed from the pre-existing tropical depression disturbance. According to China's statistics, the tropical cyclones in the western Pacific-South China Sea region come from four initial disturbances in intertropical convergence zone, accounting for 80% ~ 85%; East wind wave, accounting for about10%; The cut-off low pressure in the long wave trough at middle and high latitudes, or the cold vortex at high altitude, accounts for about 5%; Baroclinic disturbance accounts for less than 5%.
The temperature and humidity of the upper and lower atmosphere in tropical oceans are mainly determined by the sea surface water temperature. The higher the SST, the higher the temperature and humidity of the lower atmosphere, and the more obvious the potential instability.
Typhoons are formed on the warm ocean surface with SST ≥ 26 ~ 27℃. Generally speaking, the global tropical ocean surface meets this condition all year round, and only the SST in the equatorial southeast Pacific Ocean is ≤ 26.5℃ all year round, which is the main reason why there are no typhoons here.