A modelling study of ice effect on tidal damping in the Bohai Sea

Abstract

Ocean tides have been reported to be significantly damped by sea ice due to the fact that the bottom of sea ice is rough and able to dissipate tidal energy. To examine this damping effect of sea ice on the astronomical tides in the Bohai Sea, where sea ice is common in winter, this study has developed a three-dimensional ice-ocean coupled model with and without sea ice to investigate potential changes in astronomical tides based on the Finite Volume Community Ocean Model (FVCOM). This newly developed model was first evaluated against field observations and remote sensing images, including water elevations and sea ice cover, and showed good agreement between the modelling results and the observed data. In using the air forcing data (2009–2010) and the default sea ice drag coefficient of 0.0075, the model results show that in the presence of sea ice, the major tidal constituent M2 is reduced by 1 cm at the top of the three bays (from north to south: Liaodong Bay, Bohai Bay and Laizhou Bay) in the Bohai Sea, but the tidal phase is almost not affected. A sensitivity run shows that the amplitude of M2 is decreased by 2 cm when increasing the drag coefficient from 0.005 to 0.01. Moreover, two extreme combinations of air temperatures and winds are simulated according to the standard deviation of wind speed and temperature over the past ten years, and the damping effects of sea ice on tides are almost negligible as well. Based on the water mass analysis, it is found that both the decreases of average volumetric flow rate for inflow and outflow due to ice through the three bays are relatively small compared to the average volumetric flow rate without ice. The convergence of the cross sectional area increases the tidal amplitude of M2, which compensates the damping effect caused by sea ice.