Dehai Song

Assessment of the MCC method to estimate sea surface currents in highly turbid coastal waters from GOCI

ABSTRACT Previous studies have demonstrated that the Geostationary Ocean Colour Imager (GOCI) could retrieve sea surface currents accurately in low-moderate turbid coastal waters, based on maximum cross-correlation (MCC) technique. However, its performance in highly turbid waters remains unclear. In this study, the MCC method is used to derive hourly sea surface currents in Hangzhou Bay (HZB) with highly turbid waters from the GOCI data, and its performance is examined by in situ measurements and model simulations. The results show that the GOCI-derived sea surface currents can catch tidal phase variations well, yet the performance of the derived velocity is not as good as the previous studies in low-moderate turbid waters. The reason may be due to the rapid deposition and resuspension processes of suspended particulate matter in high turbidity waters, which contaminate the MCC pattern tracking. The GOCI-derived deposition and resuspension rates can reach up to about 190 and 270 mg l–1 h–1 in HZB, respectively, which demonstrates that the potential of geostationary ocean colour imagery in deriving the suspended particle deposition and resuspension rates.

Contributions of different tidal interactions to fortnightly variation in tidal duration asymmetry

The general framework for identifying tidal duration asymmetry proposed by Song et al. (2011) is extended to express fortnightly variability in duration asymmetry. The extended metrics are verified and studied using observed sea-level data at 481 stations worldwide. The results reveal that fortnightly variability is universal and that duration asymmetry can be stronger during neap tide than during spring tide. The fortnightly variability in duration asymmetry is primarily induced by three types of tidal interactions: interactions within the principal tidal constituents, interactions between high-frequency and principal tidal constituents, and interactions between long-period and principal tidal constituents. Among these interactions, the first type is most important at most of the stations and is related to the form number F. The contributions of different interactions can be quantified using their frequencies, amplitudes and phases. Global patterns of the fortnightly variation are illustrated using TOPEX/Poseidon altimetry data. The findings show that remarkable fortnightly variation in the tidal duration asymmetry occurs in most open oceans and is significant around an amphidromic point. The metrics derived in this study can be used to examine any time-varying characteristics in tidal asymmetry (not limited to duration asymmetry) by selecting a suitable frequency threshold. This article is protected by copyright. All rights reserved.

Calculation of city total maximum allocated load of total nitrogen for jurisdictions in Qingdao, China: A water quality-based modeling approach

This study aims to provide a quantitative basis for the precision emission reduction of land-based total nitrogen (TN) pollutants in Qingdao, China. The total maximum allocated load (TMAL) of TN pollutants within jurisdictions in Qingdao was calculated by using a 3D hydrodynamic-water quality model and a linear programming model. The TMAL includes emission TMAL, point-source and nonpoint source TMAL, TMAL removed by municipal sewage treatment system (MSTS), and soil-retained and water-retained TMAL, which were calculated after the division of source units, establishment of the land-based TN load matrix, simulation of the concentration response matrix, setting of a dissolved inorganic nitrogen (DIN) concentration control standard in the Qingdao coastal area, and calculation of TMAL. In the reliability analysis, a concentration under TMAL was considered to indicate satisfactory water quality criteria (relative standard deviation = 17%, Kappa = 0.55). The results showed that the emission TMAL density of nitrogen pollutants in source units was 1.8 ton/km2/a. Nonpoint and point source-produced TMAL densities were 17.0 ton/km2/a and 5.2 ton/km2/a, respectively. MSTS-removed TMAL density was 12.2 ton/km2/a. Soil- and water-retained TMAL were 4.0 ton/km2/a and 0.7 ton/km2/a, respectively. The summed F(D)∗ proportions of 10 districts were, in descending order, Huangdao (22%), Laoshan (21%), Jimo (18%), Shibei (13%), Licang (7%), Pingdu (7%), Jiaozhou (4%), Shinan (3%), Laixi (3%) and Chengyan (2%).

Effects of Wave–Current Interactions on Suspended-Sediment Dynamics during Strong Wave Events in Jiaozhou Bay, Qingdao, China

AbstractWave–current interactions are crucial to suspended-sediment dynamics, but the roles of the associated physical mechanisms, the depth-dependent wave radiation stress, Stokes drift velocity, ...

Tidal distortion caused by the resonance of sexta‐diurnal tides in a micromesotidal embayment

Double high water and double-peak flood current were observed in Daya Bay (DYB), China, which is a shallow, mixed, mainly semidiurnal-tide dominated bay with a micro- to meso-tidal range. Harmonic analysis reveals that the quarter- and especially the sexta-diurnal constituents are getting much stronger as tides propagating into the bay. The astronomical tides induced tidal asymmetry is yet dominant at the bay entrance, but overtaken by the sexta-diurnal tides at the end of the bay. Both the M4 and M6 tide meet the requirement proposed in previous studies, but still unable to produce a double high water alone. Therefore the conditions to produce a double high water between a fundamental tide and its higher harmonics need to be revisited. Analytical solutions were obtained in this paper, which fit the numerical solutions very well. Modelling result indicates M6 alone with M2 can produce the double high water in DYB, but limited in some regions; while the combination of M2, M4 and M6 tides would enhance the capability. The amplification of sexta-diurnal tides in DYB is dominated by resonance, and followed by shoaling effect. Bottom friction damped M6 a lot, and largely confined its amplification. However, the quadratic friction and other nonlinear processes are just responsible for about 10% of the total M6 increase. This article is protected by copyright. All rights reserved.