A case study on the rainfall distribution over the Japan Islands associated with the approach of Ty0423 in late October (Comparison with that for Ty0418)

Abstract

Rainfall distribution in the Japan Islands associated with the approach of Typhoon No.23 around 20 October 2004 (referred to Ty0423, hereafter) showed considerably different features from those in late summer of this year. The present study examined the detailed rainfall features around the Japan Islands brought by Ty0423 and the atmospheric processes based on the operational observation data by the Japan Meteorological Agency (JMA), comparing with those in association with Ty0418 around 7 September 2004. During the stage when Ty0423 was approaching or landing on the western part of the Japan Islands, the areal mean precipitation from Kyushu to Kanto District attained much larger than that for Ty0418, with wider extension of the area with the large amount of precipitation. It is interesting that, although the intense rainfall was observed only at the upstream side of the mountain range from Kyushu to Honshu District for Ty0418 except for the area near its center, strong rainfall with 10~30 mm/h persisted in wider regions from the western to the eastern part of the Japan Islands, resulting in the considerably large total rainfall for Ty0423. As for the case for Ty0423, the surface front with stable frontal surface was located just to the east of the Ty0423 center just before its landing at the Japan Islands. Thus, the huge moisture inflow mainly in the eastern region from the typhoon center seems to be redistributed widely over the Japan Islands area associated with the large-scale convergence around the stable frontal surface. In late October, the colder air associated with the high pressure system in the eastern Siberia can cover the northern part of the Japan Sea area as the seasonal march. Such basic field might be favorable for sustaining the synoptic-scale front just around the southern coast of the Japan Islands, even when the strong southerly wind invades associated with the typhoon approach there