Inter-annual variations of the ocean mixed layer in the region south of the Kuroshio Extension

2019 Fiscal Year Final Research Report

• Project/Area Number: 16K05553
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Meteorology/Physical oceanography/Hydrology
• Research Institution: Tokyo University of Marine Science and Technology
• Principal Investigator: Iwasaka Naoto 東京海洋大学, 学術研究院, 教授 (60211760)
• Project Period (FY): 2016-04-01 – 2020-03-31
• Keywords: 黒潮続流南方海域 / 冬季混合層 / 海面熱フラックス / 海洋上層成層度 / 10年規模現象

Outline of Final Research Achievements

We investigated inter-annual variations of the oceanic winter mixed layer in the region south of the Kuroshio Extension using FORA-WNP30, which is a reanalysis product of a eddy resolving ocean model. After quality evaluations of the reanalysis product, we revealed inter-annual variations of the depth, temperature and salinity of the mixed layer in the region.　We confirmed the facts that the surface heat flux anomaly was a major controlling factor of the mixed layer variations in the region in winter before 1995, which had been pointed out by Iwamaru et al. (2010), which was conducted using hydrography data only. Our study indicated that strength of the stratification of the surface layer in the previous autumn had dominated the winter mixed layer depth After 1995 winter while the contribution of surface heat flux had become smaller.

Free Research Field

海洋物理学

Academic Significance and Societal Importance of the Research Achievements

渦解像数値海洋モデルのプロダクトであるFORA-WNP30の解析から、1990年代半ばを境に黒潮続流南方海域冬季混合層深度変動に寄与する要因が海面熱フラックスから海洋上層の成層度に変わったことを確認したことは、亜熱帯循環系北西部の亜表層中層の10年規模変動現象のメカニズムを考える上で重要な手がかりを得たと言え、海洋物理学的な意義がある。また、FORA-WNP30は十分現実の海洋を再現し、様々な現象を明らかにする上で重要なプロダクトであることを示すことが出来たことは、再解析の意義を知らしめるものである。