A three-layer ocean model was used to investigate the impact of grid resolution, bottom topography, wind, throughflow (the Tsushima Warm Current) and deep water formation (DWF) forcing on deep circulation in the East/Japan Sea. High grid resolution (1/36°) and real bottom topography are essential to capture the observed features of surface and deep circulation. The bi-harmonic horizontal viscosity of the momentum equation and the horizontal diffusion of the interfacial elevation of the conservation equation both had a significant effect on the simulation of deep circulation. An increase of grid resolution from 1/12° to 1/36°, wind and DWF forcing dramatically increase the current velocity and eddy kinetic energy (EKE) of the lower-layer. Of the three forcings, the influence of wind forcing is the most powerful on the abyssal circulation, followed by the order of the throughflow and DWF forcing, respectively. DWF forcing does not largely change the horizontal circulation pattern of the lower-layer in the 1/36° resolution model, but it increases the current velocity by 33.9%. The available potential energy (APE) of the first interface and the kinetic energy (KE) of the lower layer showed seasonal variations in the northern East/Japan Sea (the Japan Basin), and there was a time lag of a maximum of 63 days between the APE peak and the KE peak. The pattern of seasonal variation in the growth rate of the baroclinic instability also coincided well with that of the APE. The APE is translated into eddies through baroclinic instability, and the eddies strengthen deep mean circulation with a shallow region on the right through eddy?topography interaction. Conversely, in comparison with the northern East/Japan Sea, the APE and the KE were relatively small in the southern East/Japan Sea (the Ulleung Basin and the Yamato Basin), and their seasonal variations were very weak. The size of the basins may cause differences in the seasonal variations in energy and in the growth rate of baroclinic instability in the northern and southern East/Japan Sea. Model results indicate that surface EKE is larger in the southern region than in the northern region of the East/Japan Sea, while deep EKE is larger in the northern area. These results are in good agreement with EKE distributions obtained from observations(the surface drifter and the ARGO float trajectories). The EKE maxima of the lower-layer is geographically concentrated on the bottom slope, indicating that the strong circulation in the lower-layer is due to the strong eddy activity on the slope. The flux calculation shows that the primary eddy fluxes of potential vorticity driving deep circulation are layer thickness flux (LAY) and relative vorticity flux (REL).

Keywords: The East/Japan Sea, Three-layer ocean model, Deep circulation of the East/Japan Sea, Deep water formation, Eddy kinetic energy, Eddy-driven circulation, Available potential energy, Vortex-length flux, Relative vorticity flux.