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Meandering Subtropical Jet and Precipitation over Summertime East Asia and the Northwestern Pacific

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タイトル: Meandering Subtropical Jet and Precipitation over Summertime East Asia and the Northwestern Pacific
著者: Horinouchi, Takeshi 著作を一覧する
Hayashi, Ayumu 著作を一覧する
発行日: 2017年 4月
出版者: American Meteorological Society
誌名: Journal of the Atmospheric Sciences
巻: 74
号: 4
開始ページ: 1233
終了ページ: 1247
出版社 DOI: 10.1175/JAS-D-16-0252.1
抄録: It has been revealed that in summertime, precipitation is enhanced to the south of the upper-level tropopausal potential vorticity contours, which are accompanied by instantaneous jets, over the eastern coastal region of China to the northwestern Pacific. It is frequently exhibited as precipitation bands ranging in size from over a thousand to several thousands of kilometers long. In this study, an analysis was conducted to quantify the relationship depending on the phase of upper-level disturbances. With composite analysis, it is shown that the enhancement along the contours occurs at all phases; it occurs not only to the east but also to the west of the upper-level troughs, although it is weaker. The midtropospheric distributions of upwelling and the Q-vector convergence are collocated with the precipitation enhancement, suggesting the importance of dynamical induction by geostrophic flow at all phases. The effects of upper-level disturbances and low-level jets (LLJs) with a southerly component are investigated by using an idealized nondimensional quasigeostrophic model supporting latent heating. While upper-level waves induce upwelling and downwelling to the east and west, respectively, of the upper-level troughs, LLJs tend to offset the downwelling, enabling precipitation to the west too. Both in the observational composite and the idealized model with LLJ, confluence and diffluence contribute to the Q-vector convergence to induce upwelling along the subtropical jet irrespective of upper-level disturbance phases. This induction is explained as a general feature of a veered jet where geopotential isolines rotate clockwise with height without requiring wind variation along the jet.
Rights: © Copyright 2017 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 September 2010 Page 2 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 website 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. All AMS journals and monograph publications are registered with the Copyright Clearance Center (http://www.copyright.com). Questions about permission to use materials for which AMS holds the copyright can also be directed to the AMS Permissions Officer at permissions@ametsoc.org. Additional details are provided in the AMS Copyright Policy statement, available on the AMS website (http://www.ametsoc.org/CopyrightInformation).
資料タイプ: article
URI: http://hdl.handle.net/2115/67243
出現コレクション:雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

提供者: 堀之内 武

 

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