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Climatological Evolution of the Okinawa Baiu and Differences in Large-Scale Features during May and June

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Title: Climatological Evolution of the Okinawa Baiu and Differences in Large-Scale Features during May and June
Authors: Okada, Yasuko Browse this author
Yamazaki, Koji Browse this author →KAKEN DB
Keywords: Mei-yu fronts
Issue Date: Sep-2012
Publisher: American Meteorological Society
Journal Title: Journal of Climate
Volume: 25
Issue: 18
Start Page: 6287
End Page: 6303
Publisher DOI: 10.1175/JCLI-D-11-00631.1
Abstract: The Okinawa baiu (summer rainy season) starts in early May and ends in late June, preceding the baiu in mainland Japan by approximately 1 month. This study investigates the time evolution of the large-scale circulation associated with the Okinawa baiu using 10-yr (1997-2006) climatologies of precipitation and meteorological fields, with particular focus on temperature advection at 500 hPa. The onset of the Okinawa baiu occurs in early May and is followed by an initial peak in precipitation during mid-May. The baiu rainband then moves southeastward, leading to a short break in baiu precipitation during late May. The rainband returns to Okinawa in early June, and a second peak in precipitation occurs during mid-June. The baiu rainband withdraws northward in late June. The mid-May precipitation peak is associated with warm advection at 500 hPa, mainly due to the meridional temperature gradient and the prevailing southerly winds. This warm advection coincides with upward motion near Okinawa; however, the warm advection is insufficient to explain the peak precipitation amount. Enhancement of precipitation by a transient disturbance probably contributes to the peak amount. The break period during late May coincides with the peak of South China Sea monsoon. Warm advection at 500 hPa strengthens again in June because of the strong zonal thermal contrast between the warm Tibetan Plateau and cold Pacific. This warm advection is able to adequately explain both the upward motion and precipitation. These results indicate that the large-scale meteorological characteristics are different during the first and second peaks.
Rights: © Copyright 2012 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at ( or from the AMS at 617-227-2425 or
Type: article
Appears in Collections:環境科学院・地球環境科学研究院 (Graduate School of Environmental Science / Faculty of Environmental Earth Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 山崎 孝治

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