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Sub-tidal barotropic current variations coupled with residual sea level fluctuation in the Bohai and Yellow Seas during wintertime are addressed in this study. The temporal evolution and spatial distribution of current fluctuation are investigated using moored acoustic Doppler current profiler data in a three-dimensional numerical model. It is found that a southward current followed by a northward current occurred in the northern Yellow Sea during the fluctuation, concurrent with a significant outflow followed by inflow through the Bohai Strait. The process is consistent from surface to bottom and is coupled with remarkable residual sea level fluctuation. This quasi three-day fluctuation with amplitude 0.2-0.3 m/s leads to 1 m/1.2 m drawdown in the northern Yellow and Bohai Seas, respectively, strongly influencing water exchange between those seas. Because this a prominent feature in the seas, it is necessary to evaluate its effect on fluctuation during winter in future studies, in particular, the northward current during the recovery phase of sea level in the Bohai and Yellow Seas regarding seasonal variation. [ABSTRACT FROM AUTHOR]

Three winter storms struck the Bohai and Yellow seas in succession during February 16-25, 2017. Periodic fluctuations of sea level, currents, temperature, and salinity were recorded at a moored station deployed in the Bohai Strait. Observations also captured significant synoptic fluctuations of inflow and outflow through the Bohai Strait with maximum magnitude exceeding 50 cm s−1. The sea level dropped by > 1 m and the bottom temperature decreased by 2.5 °C in < 30 h during these winter storms. A regional ocean model was used to investigate the prominent fluctuations of synoptic exchange flow through the Bohai Strait. The model results indicated that the Bohai and Yellow seas in their entirety responded strongly to the storm bursts and subsequent relaxation at the synoptic scale. The periodic winter storm bursts and relaxation excited the cyclonic propagation of coastal-trapped waves around the Bohai and Yellow seas. Strong periodic inflow and outflow during the passage of the three successive storms promoted water exchange between the Bohai Sea and the northern Yellow Sea. Successive winter storms might also affect the mean current structure through the Bohai Strait. The mean currents through the Bohai Strait during the studied storm period were characterized by inflow in both northern and southern parts of the strait and outflow through the middle of the strait. This arrangement is different from the traditional view of inflow via the northern channel and outflow through the southern channel. [ABSTRACT FROM AUTHOR]