Impact On The East China Seas From Wind And Other Exterior Forcing

Based on the physical characteristics of the East China Seas (ECS), various methods are applied to analyze the influence of wind, as well as other exterior forcing on shelf seas. Many phenomena are considered and from the point of energy transforming, the hypostasis of these phenomena are concluded by looking into the observations and numerical model results.During winter time, strong northerly wind controls the ECS. Water in most areas is well mixed and the isotherms are almost vertical to seabed. The horizontal structure of sea surface temperature (SST) is identical with the structure of isobaths, which can be explained by the one-dimensional bathymetric-control mechanism, with exception of some convection or upwelling area. During summer time, thermocline appears in the ECS, and the upper-layer mixing is mainly controlled by wind. Thus, the mixed-layer depth is mainly determined by the intensity of wind. The one-dimensional bathymetric-control mechanism still has some effects in some areas where thermocline exists. Sometimes, the intense wind distinctly induces stronger cooling and reinforces the vertical mixing. It can obviously make the mixed-layer thicker and reduce the temperature difference from bottom to surface.General circulation structures in both the Yellow Sea and the East Sea are mainly controlled by the Kuroshio (KC) and local wind. The KC gives birth to the southward Korean Coastal Current(KCC), indirectly via the Tsushima Warm Current(TSWC), and further induces the northward Yellow Sea Warm Current (YSWC) to compensate the mass loss in north Yellow Sea. This contributes about 2/3 of the YSWC. The effect of wind is also important, which induces about 1/3 of the YSWC by pushing the Chinese Coastal Current (CCC) southward. Besides, the monsoonal forcing dominants the seasonal variability of the YSWC mainly via the CCC.The speed of the energy from wind to the ECS can be calculated in the form of Ekman wave, which depends on the frequency of the wind stress. The Ekman wave travels in the z direction with amplitude decreasing exponentially with depth while energy in near-initial frequency decreases very little. The energy flux is dependent on the water depth when the wind stress is stable. The shallower the water is, the less energy wind transports. The energy flux also has relationships with the rotation of the wind. From calculating, the total energy from wind to the Ekman layer in the ECS is about 2.5GW in winter and 4.3GW in summer using the QSCAT wind vector data with a cutoff frequency of 0.5cpd. Based on the mixed-layer depth from observations, about 2.36GW can reach the bottom of the mixed-layer, more than 1/2 of the energy obtained from wind. Considering the net heat flux in different season, about 15% of the energy from wind can transform to the Gravitational potential energy(GPE). The anomaly of gravitational potential energy (GPE) would induce the anomaly of circulation. In the north hemisphere, the water moves from the region with the greater increase of GPE to that with smaller increase or decrease of GPE. So there appears a clockwise current anomaly around the region where the increase of GPE is larger and an anticlockwise current anomaly around that with smaller anomaly of GPE due to the Coriolis force. This is the channel of the energy transfer from small-scale turbulence to large-scale motions.