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As an important part of the Indo-Pacific warm pool, the Indian Ocean has great significance for research on the Asian monsoon system and global climate change. From the 1960s onward, several international and regional programs have led to important new insights into the Indian Ocean. The eastern Tropical Indian Ocean Observation Network (TIOON) was established in 2010. The TIOON consists of two parts: large-scope observations and moored measurements. Large-scope observations are performed by the eastern Tropical Indian Ocean Comprehensive Experiment Cruise (TIO-CEC). Moored measurements are executed by the TIOON mooring array and the hydrological meteorological buoy. By 2019, 10 successful TIO-CEC voyages had been accomplished, making this mission the most comprehensive scientific investigation in China. The TIO-CEC voyages have collected temperature/salinity profiles, GPS radiosonde profiles, and other observations in the Indian Ocean. To supplement the existing buoy array in the Indian Ocean, an enhanced TIOON mooring array consisting of eight subthermocline acoustic Doppler current profiler (ADCP) moorings, was established since 2013. The TIOON mooring equipped with both upward-looking and downward-looking WHLS75K ADCP provide valuable current monitoring information to depth of 1,000 m in the Indian Ocean. To improve air–sea interaction monitoring, two real-time hydrological–meteorological buoys were deployed in 2019 and 2020 in the equatorial Indian Ocean. A better understanding of the Indian Ocean requires continuous and long-term observations. The TIOON program and other aspiring field investigation programs will be promoted in the future. [ABSTRACT FROM AUTHOR]

Acoustic Doppler current profiler (ADCP) echoes can be transformed into mean volume backscattering strength (MVBS), which is positively proportional to the biomass of zooplankton and micronekton. A mooring with an upward-looking 75-kHz ADCP was deployed on the northern slope of the South China Sea to monitor diel vertical migration (DVM) and vertical distributions of zooplankton and micronekton under general conditions and extreme conditions such as typhoons. DVM occurs throughout the year, with the maximum migrating speed reaching 9.0 cm s−1. It had some cyclic variation, which was in response to marine environment and astronomical influence. Light initiates the ascents and descents of the migrators, and migration intensity may be proportional to the solar altitude. Neap-spring tidal cycle and full moon phase influences are prominent, and the peak at 112 d may be driven by variation of currents. In addition, 270 m is the demarcation between upward and downward migrations; some organisms living below this layer, especially zooplankton and micronekton, migrate to the surface to obtain nutrients and energy; other marine mesopelagic organisms also survive in this manner. Super and severe typhoons reduced vertical migration, having less influence on the deep scattering layer. As Super Typhoon Rammasun passed by the mooring station, current speed increases and temperature decreases were synchronous with changes in the deep scattering layer; the migrators swam downward to evade the influence of a higher-speed current rather than swam upward to compensate for the decrease of temperature. [ABSTRACT FROM AUTHOR]

With increasing computing power over the last decade, eddy‐resolving methods in hydraulics engineering have been widely used to investigate the turbulence structure in natural rivers, where accurate field measurements were difficult to conduct and investigate. A detached eddy simulation (DES) model was developed on the basis of the k‐ω‐SST (shear stress transport) eddy‐viscosity model within the framework of an unstructured‐mesh Semi‐implicit Eulerian–Lagrangian Finite Element (SELFE) hydrodynamic model. The DES model was then applied to simulate the bend flow in the upper Yangtze River, and the calculation efficiency was enhanced through parallelized computation to mitigate the high computation costs involved in the DES modelling. The time‐averaged velocity, turbulent intensity and Reynolds stress were compared, using DES modelling and acoustic Doppler current profiler (ADCP) measuring results, indicating good agreement, especially in the near‐bed region. The coupled relationship between the turbulent flow and riverbed terrain was also investigated through extracting and analysing the high‐order statistical variables reflecting the turbulence structure, including non‐hydrostatic pressure, vorticity and helicity, indicating the fluctuated amplitude of non‐hydrostatic pressure can reach to 100 Pa, and the stripe distribution of non‐hydrostatic pressure and vorticity had an orthogonality relation. At the same time, the streamwise velocity at the middle of the HLM bend was found to be decreased at least 0.7 m/s because of unsteady process smoothing and backwater effects attributable to water releases and storage of the reservoirs located upstream and downstream of the HLM bend. The developed unstructured‐mesh DES model will provide a new tool to study turbulent flows in a natural river and assess the effect of reservoir operations on river flows. [ABSTRACT FROM AUTHOR]

Xiao, K.; Li, H.; Song, D.; Chen, Y.; Wilson, A.M.; Shananan, M.; Li, G., and Huang, Y., 2019. Field measurements for investigating the dynamics of the tidal prism during a spring-neap tidal cycle in Jiaozhou Bay, China. Journal of Coastal Research, 35(2), 335–347. Coconut Creek (Florida), ISSN 0749-0208. The tidal prism is a crucial environmental index for evaluating the water self-purification capacity in semi-enclosed bay systems, but quantitative studies linking spring-neap tidal variations are few. In this paper, field measurements of the tidal level and tidal flux were conducted in Jiaozhou Bay (JZB) to estimate the hydrodynamic and tidal prism variations during a spring-neap tidal cycle. JZB is located on the south coast of Shandong Peninsula, China, with a narrow inlet of 3.1 km width, which was accessible for continuous shipboard Acoustic Doppler Current Profiler measurements over 15 days. Unfortunately, due to the violent sea induced by typhoon "Chan-hom," the measurements were suspended for 2 days. However, the fluxes during the temporary suspension were reproduced using the significant linear relationship between the inlet fluxes and the changes in tidal level (r2 = 0.94, P < 0.001), without considering the storm surge. The relationship between tidal range and tidal prism was also linearly correlative (r2 = 0.69, P < 0.001), indicating that the tidal prism was primarily controlled by the tidal range in JZB. These linear relationships are well verified by historical data in JZB. Compared with previous studies in JZB, the tidal prism has decreased 26% from 1928 to 2008. The decreased intertidal areas, caused by large-scale land reclamations, were likely responsible for the decrease in the tidal prism, which in turn weakened the self-purification capability and triggered the chronic pollutant enrichment. However, the tidal prism increased 4% from 2008 to 2015 as the restoration of water area through protective policies formulated by government. These findings will contribute to designing maintenance strategies for reducing human activity impacts on the health of JZB in the future. [ABSTRACT FROM AUTHOR]

How flow mixing process influences the wetlands of the Yangtze Estuary is still poorly understood. Hydrological fieldwork was conducted on five vessel-anchored sites (S1-S2; M1-M2-M3) near the major wetlands of the Yangtze Estuary offshore (121°57′-122°30′E, 30°50′-31°23′N) on May 8-11 2004, to examine the dynamics of neap tides in the non-flood season of the Yangtze (∼24, 700 m 3 s -1 at Datong) and their impacts on adjacent wetlands. Based on the measurement of the acoustic Doppler current profiler (aDcp), direct-reading current meter and optical backscattering sensor (OBS-3A), two flow patterns were revealed: 1) well mixing flow pattern caused by the turbulent tidal currents, and 2) weak mixing flow pattern resulted by the estuarine circulation in the North Port of the estuary. The characteristics of such different flow patterns were analyzed and resultant sediment dispersals were discussed in relation to the adjacent wetlands. It is suggested that the estuarine circulation might be the important process to nourish the eastern wetland of the Yangtze Estuary which has been neglected before. [ABSTRACT FROM AUTHOR]

Field observations were conducted at an inflection point of two bends of the Oujiang River Estuary, China, to investigate lateral circulation and its driving mechanisms, and the effect of stratification in a macrotidal estuary. Repeated cross-channel transect measurements of velocities were obtained by vessel-mounted acoustic Doppler current profiler at the inflection point during neap and spring tides. Conductivity, temperature, and depth were collected at both ends of the transects to estimate the lateral moment budget. We observed asymmetry of lateral circulation in intra-tidal and inter-tidal regions, with strong single-cell lateral circulation during the neap ebb tide. In contrast, during the flood, lateral circulation was weak but structurally complex. During the spring tide, lateral circulation only appeared at peak ebb and peak flood. This asymmetric variation in lateral circulation is induced by an asymmetric driving mechanism, investigated thoroughly and connected to water stratification. The significant effect of nonlinear advective acceleration in both highly stratified water and well-mixed water indicates the important influence of an inflection point of two bends on lateral circulation. Besides, the strong stratification plays a role to suppress the lateral circulation due to the tilted pycnocline spin opposite to lateral circulation. The Oujiang River Estuary is an important shipping area, and the results have practical significance for the development and utilisation of port and channel resources. • Field data were collected at an inflection bend of the Oujiang River Estuary. • Cross-channel measurements of current velocity obtained by vessel-mounted ADCP. • Strong, asymmetrical lateral circulation occurs during the neap ebb tide. • During the flood, lateral circulation is weak but structurally complex. • Findings have practical significance for port and channel resources. [ABSTRACT FROM AUTHOR]

China's largest freshwater lake, Poyang Lake, is characterized by rapid changes in its inundation area and hydrodynamics, so in this study, a hydrodynamic model of Poyang Lake was established to simulate these long-term changes. Inundation information was extracted from Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing data and used to calibrate the wetting and drying parameter by assessing the accuracy of the simulated inundation area and its boundary. The bottom friction parameter was calibrated using current velocity measurements from Acoustic Doppler Current Profilers (ADCP). The results show the model is capable of predicting the inundation area dynamic through cross-validation with remotely sensed inundation data, and can reproduce the seasonal dynamics of the water level, and water discharge through a comparison with hydrological data. Based on the model results, the characteristics of the current velocities of the lake in the wet season and the dry season of the lake were explored, and the potential effect of the current dynamic on water quality patterns was discussed. The model is a promising basic tool for prediction and management of the water resource and water quality of Poyang Lake. [ABSTRACT FROM AUTHOR]

To study cohesive sediment behaviors and their time-variability in the near-bottom layer in the muddy area of the northern Taiwan Strait (TS), a short-term bottom-mounted tripod, which was equipped with an acoustic Doppler velocimeter (ADV), an upward acoustic Doppler current profiler (ADCP) and a CTD with a Seapoint turbidity sensor, was deployed at the northern TS over seven days between July 22 and 29, 2012. The near-bed current velocity, wave orbital velocity, bottom shear stress induced by wave and current, near-bed suspended sediment concentration (SSC) and variations in the bed elevation were resolved. The observation results indicate that the most important semidiurnal constituent at the northwest TS is M 2 and that the near-bed (0.7 mab) current speed showed spring-neap cyclic characteristics, with a maximum value of 0.453 m/s. Additionally, the water flowed in acounter-clockwise rotary current pattern. The weather was fair during the observation, and the significant wave height ranged from 0.60 m to 1.81 m, which generated an extremely low wave orbital velocity (the maximum value was 0.128 m/s). The near-bed SSC estimated from the signal-noise ratio recorded by the ADV ranged from 1.48 mg/L to 74.95 mg/L. The relation between the bottom shear stress and the SSC suggested that the local sediment resuspension is primarily controlled by a tidal current and that the wave action was practically negligible during the observation. The resulting net near-bed horizontal transport flux was 1387.59 kg/m 2 during the observations, dominated by the along-shelf flux (approximately 3.74 times than cross-shelf flux) and directed toward the NNE. The bed elevation revealed that the mean value of the erosion and deposition depth during a tidal cycle could reach 14.8 mm in an intermediate tide, with a maximum value of 17.9 mm; the net effect during the observation was erosion, with a depth of 0.4 mm. [ABSTRACT FROM AUTHOR]

Establishing a suitable location for a fish collection system is crucial for luring and collecting fish and requires the swimming characteristics of fish to be considered. This study aimed to identify a suitable location to lure fish to the fish collecting system (or barge) on the Hong River. For this purpose, a 3D computational fluid dynamics model for the downstream of dam was verified using Acoustic Doppler current Profiler (ADCP) velocity data to simulate the flow field of river channel considering of seven typical operation scenarios. The swimming performance of five endemic fish (Bagarius rutilus, Cyprinus carpio rubrofuscus, Semilabeo obscures, Channa argus, and Opsariichthys bidens) were evaluated using three indexes, i.e., induced flow velocity, critical swimming speed, burst swimming speed, to determine their migration behavior zones by analyzing different flow velocities. By adapting the simulated flow fields in each operation scenario, potential fish migration aggregation zones were analyzed. The results suggested that the most optimal position for placing the FCP was in the left bank of river channel at X = 400–500 m in typical operation scenarios. This study provides a reference for designing FCP for fish pass facilities that combine fish swimming behavior and hydraulic variables of the river channel. [ABSTRACT FROM AUTHOR]

We investigated spatial relationships between barotropic tidal currents and tides (i.e., tidal elevations) in the tidally predominant Yellow and East China Seas and Korea Strait (YESKS) continental shelf region to understand which tidal current and tide (TCE) characteristics underpin essential insights for maritime search, rescue and recovery operations. As baseline information for such operations, tidal current types were classified using FES2014 model TCE harmonic constant data and phase lag relationships for the predominant M 2 constituent, to determine maximum flood currents. In terms of surface current spatial variation, the M 2 currents were classified into three types: standing, progressive, and mixed tidal waves. In addition to these horizontal patterns, Acoustic Doppler Current Profiler (ADCP) records from three stations on the west coast of Korea during summertime 2007 and wintertime 2015 were harmonically analyzed to reveal the vertical structure of M 2 constituent tidal currents, including ellipse parameter gradients. M 2 tidal current types were found to vary through the water column, with the maximum tidal current delayed by up to 40° (∼1.4 h) in near surface waters compared to bottom waters. M 2 tidal current types also varied vertically, with changes in its ellipse phase: for example, from a near-surface mixed tidal wave to a standing tidal wave near the seabed. Finally, to explore other TCE conditions relevant to rescue and recovery operations, distributions of the age of the tide and of the tidal current ellipse were compared, with results exhibiting similar distributions for both parameters, including >1.5 days in the Yellow Sea and <1.5 days in Korea Strait. In conclusion, as demonstrated by the spatially and vertically complex tidal current type patterns found in the YESKS, detailed three dimensional understandings of TCE processes are needed to successfully support maritime search, rescue and recovery operations in this and other regions. • Maritime search and rescue and salvage operations can be improved via analysis of optimal tidal current conditions. • A simple method is provided for calculating maximum ebb and flood current velocities. • Analyses are based on the phases and amplitudes of the M 2 tidal currents and tides. • Tidal currents are classified across the tide-predominant Yellow and East China Seas and Korea Strait (YESKS) region. [ABSTRACT FROM AUTHOR]

Aimed at the explanation of clear tidal signal and storm surge signals in a closed inland lake near the coast (the Huguangyan Lake), this work uses a combined approach with observations and model experiments. Huguangyan Lake is a closed inland freshwater coneless volcanic crater lake near the coast in tropical southern China, less than 5 km from an estuary. It has a diameter of about 1.5 km and relatively deep water of up to 20 m. Bottom pressure was measured from an acoustic Doppler current profiler (ADCP) for 10 days in September 2018 and 10 days in January 2019. The observations encompass the period of Typhoon Mangkhut, which passed the region when it made its landfall. The time series demonstrate clear tidal and subtidal signals. The tidal signal remains even if we exclude the barometric pressure effect. Interestingly, the lake has no surface connection with the ocean. The astronomical tide has an amplitude of about 2 cm. The major tidal signals include the principal solar semidiurnal (S2) and lunisolar (K1) constituents. During the passage of Typhoon Mangkhut, the water level variability inside the lake increased by an order of magnitude (>0.3 m). To examine whether the lake water level change was due to the natural oscillations inside the lake (or seiche), a numerical wind-driven hydrodynamics model was designed using the 3-D Finite Volume Community Ocean Model (FVCOM). The results show that a small first-order seiche can be generated, but only with a time scale of minutes and with a magnitude much smaller than the observed surface elevation changes. This excludes any measurable seiche and the observed surface elevation change inside the lake cannot be wind-driven. Moreover, tides inside the lake are not generated by tidal potential, as the lake is too small for having a locally generated tide. The main result of our study has therefore excluded the local tidal-generating force, wind-driven seiche, and barometric effect, as possible causes of the lake oscillation which has tidal and subtidal signals. The subtidal variation is at least one order of magnitude greater than tides inside the lake and is caused by weather-induced overall coastal ocean water level oscillations transmitted into the lake through groundwater connection. All these lead to the major conclusion that the lake is connected to the coastal ocean through groundwater. [ABSTRACT FROM AUTHOR]