Abstract
1. Warm air is flowing as a jet stream in the upper and lower layer when a typhoon is approaching. This jet stream height is of maximum vertical velocity.
2. The jet stream proceeds some hundreds kilometers ahead the typhoon, and causes heavy rainfall. The rainfall amount is controlled by the mixing ratio at the jet stream height.
3. Typhoon rain consists of two kinds, one is vortical in nature and the other moves north as a wave-like disturbance.
4. The rainfall due to the wave-like disturbance is proportional to the net time change of eu, where e is the vapour tension and u the horizontal velocity, which shows that this rainfall is due to the line of convergence.
The vortical rainfall occurs at the place of vorticity accumulation and moves with vorticity.
