1993 Volume 48 Issue 1 Pages 20-32
Regional difference and variability of precipitation during the Baiu season (June and July) in East Asia have been studied preliminary in terms of the frequency distribution of daily precipitation and the precipitation brought about in each precipitation intensity class determined empirically. In order to demonstrate the spatial distribution of dominant daily precipitation amount (class), cluster analysis was conducted using the contribution ratios of the precipitation brought about in respective classes to total precipitation at each station using the data from 1977 to 1981. The 234 stations were classified into eight groups. Regional division was conducted based on this classification of stations. South-west Japan, Korean Peninsula and Central China Plane where the Baiu phenomenon is predominant were identified as same group. In these regions, considerable amount of total precipitation is brought about by heavy rainfalls greater than 50 mm/day. The class of maximum contribution ratio shifts heavy rainfall side with increasing of regional averaged total precipitation. Nevertheless, the class of the miner peak appears in 15-30 mm/day independently with the total precipitation amount. This fact suggests the existence of the rainfall system that causes almost the same precipitation to the comparatively rainy regions as well as the peculiar rainfall system to the region that controls total precipitation. Moreover, relationship between frequency distribution of daily precipitation and total precipitation was analyzed preliminary in terms of inter-annual variation using the data from 1951 to 1990 at Shionomisaki in the South-west Japan and Akita in North-east Japan. The result indicates that the variation of Baiu precipitation is caused not orLly by the simple variation of number of rairLfail days but variation of proportion of heavy rainfall days to total rainfall days and whether extremely heavy rainfall appears or not, corresponding to the rank of total rainfall amount. This suggests that the wide range variation in precipitation consists of multiple backgrounds that control precipitation variations of respective ranges.