Simulation of eddy-driven deep circulation in the East/Japan Sea by using a three-layer model with wind, throughflow and deep water formation forcings

• Deep circulation of the East (Japan) Sea comparable to observed data is simulated by using three-layer numerical model with high horizontal grid resolution.
• The roles of the external forcings (wind, Throughflow, deep water formation) and real bottom topography are studied for the abyssal circulation of the East Sea.
• 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.
• We find that the primary eddy fluxes of potential vorticity driving cyclonic eddy-driven deep circulation are layer thickness flux and relative vorticity flux in the East Sea.

A three-layer 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. 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%. 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 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).