A heavy precipitation event occurs along the Ibuki-Suzuka Mountains that locates in the west of the Nobi Plain, Japan on 2-3 September 2008. Maximum total precipitation amount observed by rain gauges is 425 mm for 18 hours. According to the Japan Meteorological Agency C-band radar (JMAradar) data analysis, the heavy precipitation event is brought about by the line-shaped stationary precipitation band for about 13 hours. This study examines that the maintenance and enhancement mechanisms of the precipitation band using two X-band polarimetric Doppler radars (X-pols) and JMAradar.

The precipitation band is formed along the mountains whose alignment is north-south direction. The length and width of the band are about 100 km, 20 km, respectively. Firstly, the low-level warm-moist southeasterly whose equivalent potential temperature is greater than 355 K would impinge on the upslope of the mountains and develop convective clouds. Secondly, the convective clouds move to north as a result of influenced by southerly at midlevel and would form the precipitation band. And the maintenance of the precipitation band would result from continuing the vertical wind profile which is the low-level southeasterly that develops the convective clouds and the southerly over an altitude 1 km that effects the northing convective clouds.

Two significant heavy precipitation areas whose horizontal scales are about 10 km appear in the precipitation band. Using the dual-Doppler analysis with X-pols, the significant heavy precipitation is induced by the continuous low-level convergence. This convergence would be attributed to the orographic effect; that is, the environmental southeasterly is impinged on a wedge shaped valley that is opened southward between the Ibuki-Suzuka Mountains and its branch (the Yoro mountains) whose alignment is north-northwest to south-southeast direction. The convergence is continuing during heavy precipitation observe. The upward flow is induced by the convergence. And the graupel is discriminated corresponding the upward flow above melting level. The significant heavy precipitation would be induced by the result that the upper graupels formed by the continuous low-level convergence become large raindrops because the graupel falls and melts.