日本地球惑星科学連合2014年大会

講演情報

口頭発表

セッション記号 A (大気海洋・環境科学) » A-CG 大気海洋・環境科学複合領域・一般

[A-CG37_28AM2] 熱帯におけるマルチスケール大気海洋相互作用現象

2014年4月28日(月) 11:00 〜 12:31 423 (4F)

コンビーナ:*名倉 元樹((独) 海洋研究開発機構)、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)、時長 宏樹(ハワイ大学国際太平洋研究センター)、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)、今田 由紀子(東京大学大気海洋研究所)、座長:名倉 元樹((独) 海洋研究開発機構)、清木 亜矢子(海洋研究開発機構)

12:25 〜 12:31

[ACG37-P03_PG] マスカリン高気圧とそれに伴う西風ジェットとストームトラックの季節変動

ポスター講演3分口頭発表枠

*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:subtropical high, Indian Ocean, Agulhas Return Current, SST front, jetstream, stormtrack

The subtropical high in the Southern Indian Ocean, called the Mascarene high, is an integral part of the climate system there, influencing not only weather conditions in the surrounding regions but also the oceanic state. The present study examines the mechanisms for the seasonal variations of the Mascarene high. The high resides over the eastern portion of the basin in summer, while it shifts westward in winter toward the Agulhas storm-track core in strengthening. This large seasonal displacement is a distinct feature of the Mascarene High from other subtropical highs. Our analysis reveals that, while low-level thermal contrasts between the Australian continent and southeastern Indian Ocean is important for the formation of the high in summer, its wintertime formation is owing primarily to eddy-feedback forcing due to the seasonally-enhanced storm-track activity that is maintained in the presence of pronounced SST gradient along the Agulhas Return Current. In winter, the mid-tropospheric subsidence over the surface high is associated with upper-tropospheric convergence of the cross-equatorial divergent flow, indicative of a connection between the high and the Asian summer monsoon. From the viewpoint of vorticity budget, the cyclonic tendency by the upper-level convergence is balanced with the westerly advection of the anti-cyclonic vorticity. While the converging upper-tropospheric flux of Rossby wave activity from lower and higher latitudes acts to reinforce the high in winter, the high itself acts as a source of the climatological-mean planetary waves with the net local divergence of the flux, which is suggestive of the importance of the high even on the hemispheric scale.