The Debris Flow Disaster Caused by Back Building Squall Lines in Hiroshima, Japan
According to the quick analysis of rain gauge data, radar echo data, and grid point value data, several characteristics related to the squall lines were found as followings, i) The squall lines were evolved near the southeast edge of the moist air band along the stationary front. The warm moist air continuously flow into the region along the edge of the northwestern Pacific high. ii) Mass of the warm moist air near sealevel was transported into the coastal area of Hiroshima through the Bungo channel, which is wedged between Kyushu Island and Shikoku Island. Both of them has mountain ranges with the height of 1500 m (880-870 hPa). The lowlevel moist air also came from North Kyushu, and the strong moisture convergence was occurred in Hiroshima. iii) The wind direction of the layer between 900 hPa and 500 hPa was nearly uniform (south west) around Hiroshima area. iv) The existence of the dry air mass both side of the squall line were able to enhance the instability and convection motion in the region.