2009 Volume 5 Pages 61-64
The synoptic-scale climatology of cold frontal precipitation systems during the passage over central Japan was investigated for 19 years (1988-2006). Cold frontal precipitation events are classified into the following three types: Widespread, Hokuriku, and Jump type. Widespread-type events, which bring precipitation throughout Japan, mainly occur in spring and autumn, and the cyclones tend to move northeastward from the central part of the Sea of Japan. The central pressure of the Widespread-type cyclones is the deepest and this type has the most moisture out of the three types. Hokuriku-type events, which bring precipitation exclusively over the Hokuriku area often appear in winter, and the cyclones move eastward from the northern part of the Sea of Japan. As a result, the isobars form in an east-west orientation over mainland Japan as the cold front arrives in the Hokuriku area. The Hokuriku-type cyclones tend to be relatively weak and there is less moisture during the events. For the Jump-type events, in which the precipitation distribution appears as precipitation bands jumping over the Kanto area, cyclones develop rapidly due to the deep trough at the 500 hPa level, changing the isobars from east-to-west to northeast-to-southwest during the events.