AUTHOR=Dong Yakang , Jiang Jinglu , Liu Xiujuan , Wang Daosheng , Zhang Jicai 

TITLE=An empirical formula of bottom friction coefficient with a dependence on the current speed for the tidal models

JOURNAL=Frontiers in Marine Science

VOLUME=10

YEAR=2023

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2023.1206024

DOI=10.3389/fmars.2023.1206024

ISSN=2296-7745

ABSTRACT=<p>Tides are of great importance for ocean mixing and nearshore ocean engineering. Bottom friction is a major factor in tidal dissipation and is usually parameterized by the bottom friction coefficient (BFC). BFC is a critical parameter in numerical tidal models and is known to vary with time and space, as calculated with measured data. However, it is difficult to accurately adjust the spatially-temporally varying BFC in numerical tidal models. Based on the relationship between the spatially-temporally varying BFC estimated by adjoint data assimilation and the simultaneously simulated current speed, an empirical formula of BFC with a dependence on the current speed is proposed. This new empirical formula of BFC is compared with several traditional empirical formulas, including the constant BFC, the Chezy-Manning BFC, and two depth-dependent BFCs. When the four principal tidal constituents (<italic>M</italic><sub>2</sub>, <italic>S</italic><sub>2</sub>, <italic>K</italic><sub>1</sub>, and <italic>O</italic><sub>1</sub>) in the Bohai, Yellow and East China Seas (BYECS) are simulated, the mean vector error between the simulated results obtained using the current speed-dependent BFC and the TOPEX/Poseidon satellite altimetry data (the tidal gauge data) is 8.81 cm (10.62 cm), which is decreased by up to 8.1% (18.2%) compared with those using the several commonly used empirical formulas of BFC. Furthermore, in the sensitivity experiments where only the <italic>M</italic><sub>2</sub> tide in the BYECS, the <italic>M</italic><sub>2</sub>, <italic>S</italic><sub>2</sub>, <italic>K</italic><sub>1</sub>, and <italic>O</italic><sub>1</sub> tides in the Bohai and Yellow Sea (BYS), and the <italic>M</italic><sub>2</sub>, <italic>S</italic><sub>2</sub>, <italic>K</italic><sub>1</sub>, and <italic>O</italic><sub>1</sub> tides in the South China Sea (SCS) are simulated, the errors between the simulated results obtained by using current speed-dependent BFC and the tidal gauge data are less than those using the other empirical formulas of BFC, further demonstrating the superiority of the current speed-dependent BFC proposed in this study. From numerical model experiments, the current speed-dependent BFC can adequately reflect the spatial and temporal variations of BFC and improve the simulation accuracy of tides, thus having a broad application scope.</p>