Severe Rainfall Events Induced by Combinations of the Traveling Rain Systems and the Stationary Line-shaped Rainbands at Isahaya Region in Nagasaki Prefecture

The line-shaped stationary rainbands over the Isahaya region in Nagasaki Prefecture, which are supposed to be generated and developed by an orographical effect of the Nagasaki Peninsula, are sometimes modified their intensity of precipitation by another traveling rain systems at their combining stage. In this paper, then, we studied two cases of heavy rainfalls which occurred over the Isahaya region due to the combination of the linear stationary rainband and a traveling rainband from west to east. The main results of this study are as follows. (1) The heavy precipitation on 23 July 1999 was induced by a cold front-type rain system associated with a tropical depression, which traveled from the west and combined with the stationary rainband over the Isahaya region, and recorded the maximum rainfall amount of 417 mm in a day. (2) The severe rainfall on 12 July 2001 also took place under the influence of a traveling rain system moving from west to east. The daily maximum of precipitation amounted to 309 mm. (3) These two events more or less suggest the probability that the Tara mountain chain, which is situated near the linear stationary rainband region and having an altitude of 1058m at the summit of Gokahara-dake, strengthens effectively the downdraft of the traveling rain clouds along the southern or southeastern mountain slopes, and then newly-born convective rain cells develop rapidly near there by the southerly humid surface wind