著者

松本 健吾 加藤 内藏進 大谷 和男

出版者

岡山大学理学部地球科学教室

雑誌

Okayama University Earth Science Report (ISSN:13407414)

巻号頁・発行日

vol.20, no.1, pp.25-34, 2013-12-27

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Rainfall characteristics and large-scale atmospheric fields on the "heavy rainfall days" (with more than 50mm/day) in the mature stage of the Baiu season (16 June ~ 15 July) at Tokyo in the eastern part of the JapanIslands were examined, based on the daily and the hourly precipitation data from 1971 to 2010.Appearance frequency of the "heavy rainfall days" at Tokyo attained only about 1/3 of that at Nagasaki inthe western Japan. Furthermore, it is noted that about half of the "heavy rainfall days" at Tokyo were relatedto the typhoon. In detail, about half of the typhoon cases were associated with the direct approach of atyphoon (referred to as Pattern A, hereafter), the other half corresponded to the situation when the Baiu frontalso stagnated around Kanto District with a typhoon to the southwest of Kanto (Pattern B).Although the contribution of the intense rainfall with more than 10 mm/h to the total precipitation waslarge in Pattern A, that with less than 10 mm/h was dominant in Patterns B and C (Pattern C: meso-α-scalecyclone on the Baiu front approaching to the Kanto District). It is noted that about half of the "heavy rainfalldays" corresponded to these pattern. In other words, unlike the localized torrential rain in western Japan, the"heavy rainfall days" due to the duration of "not-so-intense-rain" appeared rather frequently in the easternpart of Japan even in the Baiu season.In both Patterns B and C, relatively strong low-level southerly wind associated with the disturbance (atyphoon or a meso-α-scale cyclone) invades into the baroclinic zone in the basic field sustained as thesowthwestern edge of the cool Okhotsk air mass. It is interesting that the "heavy rainfall days" there due tothe contribution of the persistent "not-so-intense-rain" occur just in such situation.