A STUDY OF THE HEAVY RAINFALL OVER THE OHSUMI PENINSULA (JAPAN) CAUSED BY TYPHOON-9307

On the night of 9 August 1993, Typhoon 9307 passed near the southern p art of Japan and caused heavy rainfall and many land-slide disasters a cross the Ohsumi Peninsula. A notable feature of this event is that th e rainfall amount was very large on the lee side of the mountains. The 9-hour rainfall exceeded 150 mm at the greater part of the stations o n the lee side, while it was only 80 mm at the station on the windward side. All the land-slide disasters occurred on the lee side. The heav y rainfall was mainly produced between the eyewall and the rainband of the typhoon. Radar echoes showed strong reflectivity over the mountai ns during the rainfall event. The rainfall increasing process was stud ied by using a two-dimensional numerical model. The results suggested that the seeder-feeder mechanism contributed to the rainfall enhanceme nt on the lee side. Namely, the precipitating particles from the upper cloud grew over the mountains by accreting cloud water produced by th e orographic lifting, and the grown particles were carried to the lee side by the strong wind of the typhoon. In addition, it was also sugge sted that the downdraft of the mountain wave made an additional contri bution to the rainfall enhancement by transporting many ice particles to the lower layer.