2018 Fiscal Year Final Research Report

Quantification of mixing hotspots in the Southern Ocean for accurate modeling of the global overturning circulation

Research Project

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Project/Area Number	15H02131
Research Category	Grant-in-Aid for Scientific Research (A)
Allocation Type	Single-year Grants
Section	一般
Research Field	Meteorology/Physical oceanography/Hydrology
Research Institution	The University of Tokyo
Principal Investigator	HIBIYA Toshiyuki 東京大学, 大学院理学系研究科(理学部), 教授 (80192714)
Co-Investigator(Kenkyū-buntansha)	羽角博康東京大学, 大気海洋研究所, 教授 (40311641) 北出裕二郎東京海洋大学, 学術研究院, 教授 (50281001) 田中祐希東京大学, 大学院理学系研究科(理学部), 助教 (80632380)
Project Period (FY)	2015-04-01 – 2018-03-31
Keywords	南大洋 / 乱流パラメタリゼーション / 南極周極流 / 風下波 / 投棄式乱流計
Outline of Final Research Achievements	Global mapping of deep-ocean mixing is crucial for accurate modeling of the global overturning circulation. In this study, we conducted microstructure observations in the Southern Ocean with wind-induced mixing hotspots which cannot be expected to exist anywhere else in the world’s oceans. We successfully obtained quite a few microstructure data from the sea surface down to the seabed using a newly developed microstructure profiler called VMP-X. Based on the results from these microstructure observations as well as accompanying numerical experiments, we next assessed the validity of the existing fine-scale parameterization of turbulent dissipation rates in the Southern Ocean. It has been shown that the existing fine-scale parameterizations tend to overestimate turbulent dissipation rates especially near the polar front of the Antarctic Circumpolar Current where mesoscale eddy activities are prominent.
Free Research Field	海洋物理学
Academic Significance and Societal Importance of the Research Achievements	温和な地球環境の維持に重要な役割を果たしている深層海洋大循環に注目し、全球にわたる海水循環を本質的に駆動する「乱流」に着目し、深層海洋大循環の維持に不可欠となる乱流のエネルギー不足に関する未解決問題である“Missing Mixing”に挑んだ意欲的な研究である。観測対象海域である南大洋は、その過酷な環境ゆえに乱流観測は非常に困難であるが、南極周極流域で最新の深海乱流計VMP-Xを使用した深度4000メートル以上の深海底にまで及ぶ乱流観測を実施し、世界初となる海面から海底直上までの乱流混合強度の鉛直プロファイルの取得に成功したことは特筆すべき成果といえる。