Editorial Type:
Article
Article Type:
Research Article

Offshore Detachment Process of the Low-Salinity Water around Changjiang Bank in the East China Sea

Jae-Hong Moon Department of Earth System Science and Technology, Interdisciplinary Graduate School of Engineering Science, Kyushu University, Kasuga-Koen, Kasuga, Japan

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Naoki Hirose Research Institute for Applied Mechanics, Kyushu University, Kasuga-Koen, Kasuga, Japan

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Jong-Hwan Yoon Research Institute for Applied Mechanics, Kyushu University, Kasuga-Koen, Kasuga, Japan

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Ig-Chan Pang Department of Oceanography, Cheju National University, Jeju, South Korea

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Print Publication:
01 May 2010
DOI:
https://doi.org/10.1175/2010JPO4167.1
Page(s):
1035–1053
Restricted access

Abstract

A patchlike structure of low-salinity water detached from the Chanjiang “Diluted Water” (CDW) is frequently observed in the East China Sea (ECS). In this study, the offshore detachment process of CDW into the ECS is examined using a three-dimensional numerical model. The model results show that low-salinity water is detached from the CDW plume by the intense tide-induced vertical mixing during the spring tide period when the tidal current becomes stronger. During the spring tide, thickness of the bottom mixed layer in the sloping bottom around Changjiang Bank reaches the mean water depth, implying that the stratification is completely destroyed in the entire water column. As a result, the offshore detachment of CDW occurs in the sloping side of the bank where the tidal energy dissipation is strong enough to overcome the buoyancy effect during this period. On the other hand, the surface stratification is retrieved during the neap tide period, because the tidal current becomes substantially weaker than that in the spring tide. Wind forcing over the ECS as well as tidal mixing is a critical factor for the detachment process because the surface wind primarily induces a northeastward CDW transport across the shelf region where tide-induced vertical mixing is strong. Moreover, the wind-enhanced cross-isobath transport of CDW causes a larger offshore low-salinity patch, indicating that the freshwater volume of the low-salinity patch closely depends on the wind magnitude.

* Current affiliation: Research Institute for Applied Mechanics, Kyushu University, Fukuoka, Japan

Corresponding author address: Jae-Hong Moon, Research Institute for Applied Mechanics, Kyushu University, Kasuga-Koen 6-1, Kasuga 816-8580, Japan. Email: jhmoon@riam.kyushu-u.ac.jp

Abstract

A patchlike structure of low-salinity water detached from the Chanjiang “Diluted Water” (CDW) is frequently observed in the East China Sea (ECS). In this study, the offshore detachment process of CDW into the ECS is examined using a three-dimensional numerical model. The model results show that low-salinity water is detached from the CDW plume by the intense tide-induced vertical mixing during the spring tide period when the tidal current becomes stronger. During the spring tide, thickness of the bottom mixed layer in the sloping bottom around Changjiang Bank reaches the mean water depth, implying that the stratification is completely destroyed in the entire water column. As a result, the offshore detachment of CDW occurs in the sloping side of the bank where the tidal energy dissipation is strong enough to overcome the buoyancy effect during this period. On the other hand, the surface stratification is retrieved during the neap tide period, because the tidal current becomes substantially weaker than that in the spring tide. Wind forcing over the ECS as well as tidal mixing is a critical factor for the detachment process because the surface wind primarily induces a northeastward CDW transport across the shelf region where tide-induced vertical mixing is strong. Moreover, the wind-enhanced cross-isobath transport of CDW causes a larger offshore low-salinity patch, indicating that the freshwater volume of the low-salinity patch closely depends on the wind magnitude.

* Current affiliation: Research Institute for Applied Mechanics, Kyushu University, Fukuoka, Japan

Corresponding author address: Jae-Hong Moon, Research Institute for Applied Mechanics, Kyushu University, Kasuga-Koen 6-1, Kasuga 816-8580, Japan. Email: jhmoon@riam.kyushu-u.ac.jp

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