- 公益社団法人 日本気象学会
- 気象集誌. 第2輯 (ISSN:00261165)
- pp.2022-046, (Released:2022-08-03)
During the autumn rainy season, typhoons located far from Japan sometimes cause significant precipitation in Japan. In this study, we characterized remote precipitation events in September for 40 years from 1980 to 2019. We also analyzed cases in which remote precipitation did not occur despite approaching typhoons, as well as cases in which heavy precipitation was not affected by typhoons. We characterized the environmental fields of the remote precipitation cases by comparing them with these other two types of cases. Statistical analysis showed that remote precipitation tended to occur when the typhoons were located over the southern or southwestern oceans of mainland Japan and when the tracks of the typhoons were northward or changing to the northeast. The composite analysis of the remote precipitation cases showed that the subtropical high was retreating to the east for the two days before the remote precipitation. By contrast, the cases in which remote precipitation did not occur showed the opposite pattern: the subtropical high was strengthening to the west when typhoons were approaching over the southern or southwestern oceans of the Japanese archipelago. Furthermore, the remote precipitation occurred to the equatorward jet streak entrance of the 200 hPa jet, whereas the 200 hPa jet streak was shifted to the west in the cases where remote precipitation did not occur. The vertical cross-section of the northward water vapor flux showed that the northward water vapor inflow from the middle troposphere was larger in cases of remote precipitation than in cases in which heavy precipitation was not caused by typhoons. In addition, dynamical analysis showed that the area of remote precipitation corresponded to the region of 800-600 hPa mean quasi-geostrophic forcing for ascent and 925 hPa frontogenesis.