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| 黑潮近岸分支流在2017年9月与2019年9月差异的研究 |
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燕杰1,2,3, 侯一筠1,2,3,4, 刘泽1,3,4
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1.中国科学院海洋研究所 海洋环流与波动重点实验室 青岛 266071;2.中国科学院大学 北京 100049;3.中国科学院海洋大科学中心 青岛 266071;4.青岛海洋科学与技术试点国家实验室 海洋动力过程与气候功能实验室 青岛 266237
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| 摘要: |
| 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，通过分析大面观测同期的绝对海表动力高度、地转流场以及海表风场的差异，阐述了黑潮近岸分支流路径产生显著年际差异的动力机制。2019年8—9月东海海表较2017年8—9月盛行更强的西南向沿岸季风，强的西南向沿岸风通过埃克曼输运促使水体向岸堆积并在近岸区域沿岸西南向堆积。因此，2019年8—9月东海近岸海域的跨岸方向压力梯度与2017年8—9月相比较小而沿岸压力梯度则较大。2019年8—9月，受压力梯度分布的影响，东海近岸海域产生西南向的沿岸地转流和离岸地转流。其中西南向的沿岸地转流会在底部生成离岸的底埃克曼流，离岸底埃克曼流和离岸地转流共同抑制了黑潮近岸分支流的向岸入侵。这导致2019年9月黑潮近岸分支流的路径向东偏移，黑潮次表层水入侵浙江近海及长江口区域的强度随之减弱。通过分析研究实际观测案例，阐述了风影响黑潮近岸分支流入侵东海近岸海域的动力机制，同时明确指出海表风场会从黑潮近岸分支流的中上游区域改变其路径，进而对黑潮入侵东海近岸海域产生重要影响。 |
| 关键词: 黑潮近岸分支流 底埃克曼流 地转流 风 黑潮入侵 |
| DOI：10.11693/hyhz20201000301 |
| 分类号:P731.26 |
| 基金项目:国家自然科学基金，41630967号，41776020号。 |
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| THE DIFFERENCE OF THE NEARSHORE KUROSHIO BRANCH CURRENT BETWEEN SEPTEMBER 2017 AND SEPTEMBER 2019 |
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YAN Jie1,2,3, HOU Yi-Jun1,2,3,4, LIU Ze1,3,4
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1.CAS Key Laboratory of Ocean Circulation and Waves, Institute of oceanology, Chinese Academy of Sciences, Qingdao 266071, China;2.College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China;3.Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China;4.Laboratory for Ocean and Climate Dynamics, Pilot National Laboratory for Marine Science and Technology, Qingdao 266237, China
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| Abstract: |
| 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. |
| Key words: nearshore Kuroshio branch current (NKBC) bottom Ekman current geostrophic current wind Kuroshio intrusion |