黑潮近岸分支流在2017年9月与2019年9月差异的研究

通过对比2017年9月和2019年9月的温盐大面观测数据,发现东海陆架上黑潮近岸分支流的路径在两次观测中存在显著差异.2019年9月黑潮近岸分支流中上游的路径相较2017年9月明显的东向偏移,造成黑潮次表层水入侵东海近岸海域的强度较弱.为了探究黑潮近岸分支流的上述显著年际差异的原因,利用卫星高度计数据和再分析风场数据,...

THE DIFFERENCE OF THE NEARSHORE KUROSHIO BRANCH CURRENT BETWEEN SEPTEMBER 2017 AND SEPTEMBER 2019

Study on the CTD (conductivity-temperature-depth) observation data of the East China Sea in September 2017 and September 2019 revealed a significant difference in the paths of the Nearshore Kuroshio Branch Current (NKBC) between the two cruises. The upper-middle paths of the NKBC in September 2019 was more eastward than that in September 2017, and the intensity of NKBC invading China nearshore area in 2019 was weaker. Satellite altimetry data and sea surface wind re-analysis data were used to explore the causes of the above-mentioned significant inter-annual differences. By comparing the differences in sea surface height, geostrophic current, and wind during the observation period of the two years, the key mechanism that induced the difference of the paths of the NKBC in September of the two years was revealed. The southwestward wind that prevailed in the East China Sea from August to September in 2019 was stronger that in 2017, The stronger southwestward wind in 2019 pushed the water to accumulate towards more shoreward and southwestward in the nearshore area. This process decreased the cross-shore pressure gradient and increased the along-shore pressure gradient in the nearshore area, and then generated southwestward alongshore geostrophic current and offshore geostrophic current. The stronger offshore geostrophic current and the offshore bottom Ekman current that induced by the southwestward alongshore geostrophic current jointly restrained the inshore intrusion of the NKBC. The mechanism resulted in the eastward migration of the NKBC, and further weakened the invasion of the Kuroshio subsurface water northward into Zhejiang coastal area and Changjiang (Yangtze) River estuary area in September 2019. Based on the analysis and research of actual observation cases, the dynamic mechanism of the influence of wind on the intrusion of the NKBC was explained, and the path variation of sea surface wind field in the middle and upper reaches of the NKBC was revealed, which had an important impact on the Kuroshio intrusion into Chinese nearshore area.