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YANG Zhitong,LUO Yiyong. 2016. Low-frequency variability of the shallow meridional overturning circulation in the South China Sea. Acta Oceanologica Sinica, 35(3):10－20

Low-frequency variability of the shallow meridional overturning circulation in the South China Sea

南海上层经向翻转环流的低频变化

Received:July 26, 2015 Revised:October 23, 2015

DOI：10.1007/s13131-016-0826-9

Key words:South China Sea meridional overturning circulation Luzon Strait transport North Equatorial Current bifurcation

中文关键词: 南海经向翻转环流吕宋海峡流量北赤道流分叉点

基金项目:

Author Name	Affiliation	E-mail
YANG Zhitong	College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao 266100, China Physical Oceanography Laboratory, Ocean University of China, Qingdao 266100, China
LUO Yiyong	Physical Oceanography Laboratory, Ocean University of China, Qingdao 266100, China	yiyongluo@ouc.edu.cn

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Abstract:

The low-frequency variability of the shallow meridional overturning circulation (MOC) in the South China Sea (SCS) is investigated using a Simple Ocean Data Assimilation (SODA) product for the period of 1900-2010. A dynamical decomposition method is used in which the MOC is decomposed into the Ekman, external mode, and vertical shear components. Results show that all the three dynamical components contribute to the formation of the seasonal and annual mean shallow MOC in the SCS. The shallow MOC in the SCS consists of two cells:a clockwise cell in the south and an anticlockwise cell in the north; the former is controlled by the Ekman flow and the latter is dominated by the external barotropic flow, with the contribution of the vertical shear being to reduce the magnitude of both cells. In addition, the strength of the MOC in the south is found to have a falling trend over the past century, due mainly to a weakening of the Luzon Strait transport (LST) that reduces the transport of the external component. Further analysis suggests that the weakening of the LST is closely related to a weakening of the westerly wind anomalies over the equatorial Pacific, which leads to a southward shift of the North Equatorial Current (NEC) bifurcation and thus a stronger transport of the Kuroshio east of Luzon.

中文摘要:

本文利用1900-2010年SODA 2.2.4版本数据,通过将MOC分解成艾克曼、外部模式(正压)和垂直剪切(斜压)三个部分,探讨南海气候态和季节性平均上层经向翻转环流的形成机制及低频变化。对于气候态经向环流的基本结构,南海北部表层顺时针经向环流圈主要决定于艾克曼部分,而外部模式部分影响逆时针翻转环流的结构,同时垂直剪切(斜压)部分对两环流圈中心有负贡献。从1900年到2010年,无论是气候态平均还是季节平均的变化,MOC强度都是呈现下降趋势,主要原因是吕宋海峡流量逐年减弱导致了外部模式部分流量的下降。进一步分析可以发现,赤道太平洋地区的西风异常减弱,会造成北赤道流向南移动和吕宋岛东部黑潮流量增强,进而导致进入吕宋海峡的流量下降。

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