Observation And Dynamical Analysis Of Jiulongjiang River Diluted Water Discharging Into The West Taiwan Strait

On the basis of the in-situ CTD data and the satellite remote-sensing turbidity data, the hydrological characteristics and the expanding patterns of the Jiulongjiang River diluted water (JDW) have been studied. The paper has also analyzed the influencing factors. Then the knowledge of fluid dynamics and a terrestrial dissolved organic matter (DOM) distribution model have been applied to reveal the dynamics of JDW. Meanwhile, the model of Regional Ocean Modeling System (ROMS) has been used to simulate the flowing patterns of the idealized JDW (IJDW) with different background coastal currents (BCCs), and investigate the dynamic response and mechanisms of the IJDW to the BCCs.After analysing the CTD data around the Xiamen Bay mouth in June and July from the year of2009to2012, the results show that during the summer cruises of2009,2010and2012, the JDW debouches into the west Taiwan Strait in the form of jets through the Xiamen Bay. Four summertime cruises data also show that during the process of expanding, there may be patch of diluted water detaching from the main route of JDW. The wintertime cruise data in November2008and February2012show that low temperature and low salinity water covers the area around the Xiamen Bay mouth in winter, however, the low salinity water is not only from the Jiulongjiang River, but also part of the Zhemin coastal current or the Minjiang River diluted water; The results also reveal that during the winter cruise of2008, JDW does not flow into the west Taiwan Strai in the form of jet.By using the knowledge of jet to analyze the CTD data, this paper indicates that: as driven by the summer southwesterly wind, the upwelling-related Dongshan low temperature and high salinity water flows northeastward in the form of jet as well. To a certain degree, the Dongshan low temperature and high salinity jet may interact with the jets formed by the JDW, and then affect the hydrological characteristics and expanding patterns of the JDW.Based on the turbidity and CTD data, there are mainly four types of spreading patterns in summer for the JDW, including (1) going northeastward along the coastline,(2) extending northeastward and southwestward at the same time,(3) just spreading out near the Xiamen Bay mouth, and (4) flowing northeastward offshore. The results also indicate that the Jiulongjiang runoff, wind, the BCCs and topography all have effect on the extending patterns.Due to the lack of current data, it is hard to quantitatively describe the influence of BCCs on the spreading of the JDW, so the ROMS is utilized to simulate the IJDW under the conditions of different BCCs. The results demonstrate that BCCs may modify the spreading patterns of IJDW. When the BCCs are less than0.10m/s, the IJDW largely flows southwestward along the coast; when the BCCs are greater than0.10m/s, the IJDW mainly spreads northeastward with an angle to the coastline. The results of model and theoretical analysis show that, when the BCCs equal to0.05m/s, the route of IJDW is almost perpendicular to the coastline, reaching a steady state. At the same time, the theoretical and momentum analysis results also indicate that with the increasing of BCCs, diluted water overlays on the BBCs and forms a two-layer vertical velocity structure with the upper layer in quasi-geostrophic balance and the lower layer in a one-way flow driven by barotropy which is balanced by the vertical viscosity term, while the effect of Coriolis term is diminished in the lower layer.