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General Session 1: Physical oceanic processes: Dynamics and physical-biological-biogeochemical interactions |
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Modeling asymmetric-tidal-mixing-induced residual flow in a periodically stratified estuary
GS1-13-S
Jianshan Mao* , College of Ocean and Earth Science, Xiamen University, Xiamen, Fujian Province, 361102,China
Peng Cheng, College of Ocean and Earth Science, Xiamen University, Xiamen, Fujian Province, 361102,China
Fengling Yu, College of Ocean and Earth Science, Xiamen University, Xiamen, Fujian Province, 361102,China
Nengwang Chen, College of the Environment and Ecology, Xiamen University, Xiamen, Fujian Province, 361102, China
Aijun Wang, Third Institute of Oceanography, State Oceanic Administration, Xiamen, Fujian Province, 361005, China
Presenter Email: mjs_mao@163.com
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Recent studies have recognized that the asymmetry of tidal mixing (ATM) between flood and ebb tides plays an important role in creating residual currents in periodically stratified estuaries. In this study we investigated ATM and its role in the dynamics of the Jiulong River Estuary, a tidally-dominated estuary in Fujian Province, China, based on a one-year numerical simulation using the Regional Ocean Model System.
The results showed that the main channel of the Jiulong River Estuary exhibits stronger tidal mixing during flood than ebb, while in the inner regime the tidal mixing asymmetry is reverse during weak tides. The ATM is stronger in the inner and central regimes than the outer regime of the estuary, and is stronger during strong tides than during weak tides.
The analysis of potential energy anomaly showed that, during strong tides, the along-estuary tidal straining produces the ATM while the lateral straining and along-estuary advection act in an opposite way that generally enhance stratification during flood and reduced stratification during ebb. However, during weak tides, as the asymmetry of tidal mixing is reversing, the lateral straining and along-estuary advection produce the ATM while along-estuary tidal straining act in an opposite way.
The decomposition of along-estuary residual circulation showed that, as a result of different transverse structure of the covariance of eddy viscosity and shear, in the inner regime, the ATM-induced flow is seaward near the surface and landward near the bottom during strong tides, which is reverse during weak tides. The magnitude of ATM-induced flow is about 2-10 times that of density-driven flow, consistent with the previous finding that ATM-induced flow is more important than density-driven flow in periodically stratified estuaries. Because the strength of ATM-induced flow is positively related to the tidal fluctuation of vertical shear and is negatively related tidal-mean vertical mixing, the strength is generally large during spring tides, could be extraordinary large during the weak neap tide of which the vertical mixing is extremely low. The ATM-induced flow has a positive correlation with the Simpson Number and the magnitude of the ATM.
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