Weibing Guan

To accurately reconstruct large-area three-dimensional current fields in coastal regions, simultaneous observations with ten coastal acoustic tomography (CAT) stations and two high-frequency radar (HFR) stations were performed in the Xiangshan Bay (XSB) on 4–5 December 2020. The section-averaged velocity that was observed by CAT and the radial velocity that was observed by HFR were, for the first time, synchronously assimilated into a three-dimensional barotropic ocean model. Compared with acoustic Doppler current profile data, the velocities of the model assimilating both CAT and HFR data had the highest accuracy according to root mean square differences (RMSDs), ranging from 0.05 to 0.08 m/s for all the vertical layers. For the models individually assimilating CAT and HFR, the values in the vertical layers ranged from 0.07 to 0.12 m/s and 0.08 to 0.13 m/s, respectively. A harmonic analysis of the model grid data showed that the spatial mean amplitudes of the M2, M4, and residual currents were 0.66, 0.14, and 0.09 m/s, respectively. Furthermore, the standing wave characteristics of the M2 current and M4 associated-oscillation in the inner XSB, mouth of the Xiangshan fjord, were better captured by the model assimilating both CAT and HFR. Our study demonstrates the advances in three-dimensional tidal current analysis using a model that assimilates both CAT and HFR data, especially in regions with complex coastal geography.

Water temperature in estuaries is sensitive to thermal discharges and expansive tidal flats; as such, this parameter is essential in maintaining estuarine ecosystem. Semi-enclosed water bodies with poor water exchange easily accumulate heat. This is especially true for Xiangshan Bay, which contains two power plants and a large area of tidal flats. This bay was used as an example to study water temperature and heat dynamics, considering the thermal discharge and tidal flats. This study developed and validated a three-dimensional hydro-heat flux numerical model using field data on tidal elevation, currents, water temperature, and tidal flat temperature. The Finite Volume Community Ocean Model combines an accurate thermal discharge model with the air-water-tidal flat heat flux model. The findings showed that thermal discharge provides heat to the bay in summer and winter, and increases the water temperature of the entire bay by 0.7°C in summer, while maintaining water temperature at 0.52°C in winter. The atmosphere and open seas had greater impacts on heat in the bay in winter and summer. The atmosphere and tidal flats provided heat to the bay in summer and absorbed heat from the bay during winter; the opposite was true for the open sea. The effect of tidal flats in summer is less than that in winter, and provides 1.31 × 10¹³ J of heat to the bay in summer, while taking 8.63 × 10¹³ J of heat from the bay in winter. This study provides a comprehensive understanding of the effects of tidal flats and thermal discharge on water temperature and heat in macro-tidal bays and estuaries; its results are applicable to similar bays around the world.

Ocean processes that can influence rapidly changing ocean color include water-mass movement and bio-optical property changes in the water parcel. Traditionally, diurnal variability of bio-optical properties relies on daily time series at fixed locations by satellite sensors or in situ observations. There is a lack of an effective way to observe diurnal variation of bio-optical properties in a moving water parcel on a large scale. In this paper, we propose a new method to acquire diurnal variation of bio-optical properties in a moving water parcel. The novel approach integrates drifting buoy data and GOCI data. The movement of surface current was tracked by a drifting buoy, and its spatiotemporally matching bio-optical properties were obtained via the GOCI data. The results in the Yellow and East China seas during the summers of 2012 and 2013 show that the variation of time series following the movement of water parcel was obviously different from that obtained at fixed locations. The hourly differences of the former are 15.7% and 16.3% smaller than those of the latter for Chl a and total suspended sediment (TSS), respectively. The value of ag₄₄₀ was more stable within the moving water parcel than in the fixed location. Our approach provides a simple and feasible way for observing diurnal variability of bio-optical properties in a moving surface water parcel.

The studies in this chapter are focused on marine ecological disasters in Jiangsu coastal area. Three kinds of algal blooms occurred in this region, namely, red tide associated with Dinoflagellate, green tide associated with Ulvaprolifera and golden tide associated with Sargassum. Numerical model results demonstrated that red tides in Haizhou Bay originated locally, because most of Dinoflagellates near Zhoushan Islands would be transported northeastward by the Changjiang diluted water, and even the lucky ones that entered the south of Jiangsu coastal area would die in the Subei Shoal due to high turbidity there. Due to the Changjiang diluted water and the prevailing southerly wind, Ulvaprolifera could not drift southward, either. Seawater with high turbidity in the Subei Shoal limited sunlight penetration into deep water column, and further inhibited the growth of Ulvaprolifera suspending in the water column. In this chapter, we use drift bottles and satellite-tracked Argos drifters to provide solid direct dynamic evidence that Ulvaprolifera could drift from the Subei Shoal to Qingdao coastal area and even further north. The sand ridges limited the traveling path of Ulvaprolifera in the Subei Shoal, and wind-driven currents and other baroclinic processes helped Ulvaprolifera travel farther to the north.

Keywords: Simulation, SAR imaging, Sand digging and heaping, The Pearl River Estuary There are frequent sand digging and heaping activities in shoal in the Pearl River Estuary (PRE). Water depth has changed in patches, which can be imaged by synthetic aperture radar (SAR). According to SAR imaging mechanism of underwater bathymetry, a 3-D hydrodynamic model is used to demonstrate the temporal variations of the shoal topography changes due to sand digging and heaping. A microwave radar imaging of oceanic surface’s program is used to simulate the variation of normalized radar cross section (NRCS) induced by the ocean surface current. The simulation is carried out to study the digging-heaping shape, water depth changes on SAR imaging of shoal bathymetry. Results indicate several points as followings. 1. Circle-shaped sand digging and heaping are imaged clearer by SAR than other shapes. 2. Sand heaping has a greater effect on SAR imaging than sand digging. 3. Bigger depth change induces bigger NRCS variation.

The hydrography, wind, Argos and Argo measurements in the areas surrounding Luzon Strait were collected. Based on the hydrographic data obtained during September 1994, the improved Princeton Ocean Model using a generalized topography-following coordinate system together with a modified inverse method was applied to study the circulation in September. Observations and the diagnostic simulation produce a consistent circulation pattern, and the main dynamical features can be summarized as follows. (1) The Kuroshio has two branches with the main Kuroshio existing above 800 m depth and the western part existing above 400 m depth. The western branch of the Kuroshio leaves the main current near 20.5°N, then flows northwestward through Luzon Strait and finally flows out of the northern boundary southwest of Taiwan, consistent with the trajectory of Argos drifters. (2) The non-linear term is important and cannot be neglected in the momentum equations in the northern part of Luzon Strait under the baroclinicity field. Using non-linear dynamics, the westward intrusion of the Kuroshio into the northern part of Luzon Strait is more curved than when using linear dynamics. However, the non-linear term is smaller and so negligible around Luzon Strait under the homogeneous density field. (3) In the area from 117°E to 119°E and from 20.2°N to 21.7°N, an anticyclonic eddy appears east of Dongsha Islands. (4) At depths above 400 m, the circulation is mainly dominated by the basin-scale cyclonic gyre. (5) In the computational domain west of 121°E, the circulation below 800 m is mainly dominated by the basin-scale anticyclonic gyre. (6) The South China Sea water flows eastward across Luzon Strait in the middle layers, then turns cyclonically, finally flowing northward into the region east of Taiwan Island, which is qualitatively in agreement with the trajectories of Argo floats at about 1000 m depth in the area east of 121°E. RÉSUMÉ [Traduit par la rédaction] Nous avons rassemblé l'hydrographie, le vent, les Argo et les mesures Argo dans les régions avoisinant le détroit de Luçon. Sur la base des données hydrographiques relevées durant le mois de septembre 1994, nous avons appliqué le modèle océanique amélioré de Princeton utilisant un système de coordonnées « suivant le terrain » généralisé de pair avec une méthode inverse modifiée pour étudier la circulation en septembre. Les observations et la simulation diagnostique produisent une configuration de circulation cohérente dont on peut résumer comme suit les principales caractéristiques dynamiques. (1) Le Kuroshio possède deux branches : le Kuroshio principal existant au-dessus d'une profondeur de 800 m et la partie ouest existant au-dessus d'une profondeur de 400 m. La branche ouest du Kuroshio quitte le courant principal aux environs de 20,5°N et se dirige vers le nord-ouest à travers le détroit de Luçon pour finalement franchir la limite nord du détroit au sud-ouest de Taïwan, ce qui correspond à la trajectoire des bouées dérivantes Argos. (2) Le terme non linéaire dans les équations est important et ne peut pas être considéré négligeable de quantité de mouvement dans la partie nord du détroit de Luçon dans le champ de baroclinité. Lorsqu'on utilise la dynamique non linéaire, l'intrusion vers l'ouest du Kuroshio dans la partie nord du détroit de Luçon est plus incurvée que lorsqu'on utilise la dynamique linéaire. Cependant, le terme non linéaire est plus petit et donc négligeable autour du détroit de Luçon dans le champ de densité homogène. (3) Dans la région allant de 117°E à 119°E et de 20,2°N à 21,7°N, un remous anticyclonique apparaît à l'est des îles Dongsha. (4) Aux profondeurs inférieures à 400 m, la circulation est principalement dominée par le gyre cyclonique à l’échelle du bassin. (5) Dans le domaine de calcul à l'ouest de 121°E, la circulation sous 800 m est principalement dominée par le gyre anticyclonique à l’échelle du bassin. (6) Les eaux de la mer de Chine méridionale s’écoulent vers l'est à travers le détroit de Luçon dans les couches intermédiaires, puis tournent de façon cyclonique pour finalement s’écouler vers le nord dans la région à l'est de l’île Taïwan, ce qui, qualitativement, s'accorde avec la trajectoire des flotteurs Argo à environ 1000 m de profondeur dans la région à l'est de 121°E.