The Mechanism of Seasonal Variation in Sea Surface Height in the Bohai Sea

The Bohai Sea, located at the edge of western Pacific, is one of the most vulnerable regions under climate change. Using the high-precision MIKE three-dimensional hydrodynamic numerical model, this study conducted comparative experiments to investigate the impacts of atmospheric pressure, wind, specific volume, and evaporation precipitation and runoff on the seasonal variations of the sea surface height (SSH) in the Bohai Sea. The findings reveal that the average annual SSH in the Bohai Sea is lower in the northeast and higher in the southwest, higher in summer and lower in winter. Moreover, the seasonal SSH variation decreases from north to south, with variations exceeding 0.4 m in the northern Liaodong Bay but only 0.2 m in the southern Laizhou Bay. Atmospheric pressure emerges as a significant factor, contributing 72.7%, 73.9%, 71.0%, and 92.0% to the seasonal SSH changes in Liaodong Bay, Laizhou Bay, Bohai Bay, and the Bohai Strait, respectively, and causing seasonal SSH difference of approximately 0.22 m in most areas. Specific volume changes contribute 6.1%, 21.7%, 19.3%, and 4.0% to the seasonal SSH variations in the respective regions. Wind direction impacts result in lower SSH in the northern Bohai Sea during winter and higher SSH in summer, while the southern part exhibits the opposite trend. This study evaluates the contribution of each factor to seasonal SSH changes, and provides reference for other areas, which improves the accuracy of engineering design and non-period water level forecasts, and evaluates potential climate changes affecting marine environments.