日本地球惑星科学連合2015年大会

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セッション記号 A (大気水圏科学) » A-CG 大気水圏科学複合領域・一般

[A-CG32] 熱帯におけるマルチスケール大気海洋相互作用現象

2015年5月26日(火) 14:15 〜 16:00 202 (2F)

コンビーナ:*時長 宏樹(京都大学防災研究所・白眉センター)、長谷川 拓也(独立行政法人海洋研究開発機構)、清木 亜矢子(海洋研究開発機構)、東塚 知己(東京大学大学院理学系研究科地球惑星科学専攻)、名倉 元樹((独) 海洋研究開発機構)、大庭 雅道(電力中央研究所 環境科学研究所 大気海洋環境領域)、今田 由紀子(東京大学大気海洋研究所)、座長:時長 宏樹(京都大学防災研究所・白眉センター)、大庭 雅道(電力中央研究所 環境科学研究所 大気海洋環境領域)

15:10 〜 15:25

[ACG32-04] 南インド洋亜熱帯高気圧の季節変動が下層雲に与える影響

*宮本 歩1中村 尚1宮坂 貴文1 (1.東京大学先端科学技術研究センター)

キーワード:マスカリン高気圧, 下層雲

Over the South Indian Ocean, there is notable seasonality in the subtropical high. In summer the high resides over the eastern portion of the basin, while it strengthens in winter and shifts westward toward the seasonally-enhanced Agulhas storm-track core. As revealed from our analysis, low-level thermal contrast between the Australian Continent and southeastern Indian Ocean is important for the formation of the high in summer, while eddy-feedback forcing due to the enhanced Agulhas storm-track activity maintained by the strong SST gradient along the Agulhas Return Current is effective for the maintenance of the high in winter. In winter a Rossby wave activity flux is convergent into the upper-tropospheric high from lower and higher latitudes.
The present study also investigates how the seasonality of the high can influence the formation of low-level clouds, which are important for the Earth's radiation budget. The MODIS satellite data reveal that stratocumulus clouds are dominant in summer off the west coast of Australia, where near-surface cold advection and descending motion are enhanced in summer with the development of the subtropical high. In winter, low-level clouds form more extensively over the subtropical ocean than in summer. To the north of the subtropical SST frontal zone, however, cumulus clouds rather than stratocumulus clouds are prevalent, owing to enhanced latent heat flux from the warm ocean under the trade winds, which is likely to induce "decoupling". Our analysis highlights the importance of the combined effect among the subtropical high, SST and its gradient in determining the local properties of low-level clouds and their seasonality.