Impact of upper ocean-topographical coupling and isopycnal outcropping in Japan/East sea models with 1/8 degrees to 1/64 degrees resolution

A regional primitive equation ocean model is used to investigate the impact of grid resolution, baroclinic instability, bottom topography, and isopycn al outcropping on the dynamics of the wind and throughflow-forced surface c irculation in the Japan/East Sea. The results demonstrate that at least 1/3 2 degrees (3.5 km) horizontal grid resolution is necessary to generate suff icient baroclinic instability to produce eddy-driven cyclonic deep mean Row s. These abyssal currents follow the f/h contours of the bottom topography and allow the bottom topography to strongly influence mean pathways of the upper-ocean currents in the Japan/East Sea. This upper ocean-topographical coupling via baroclinic instability (actually a mixed baroclinic-barotropic instability) requires that mesoscale variability be very well resolved to obtain sufficient coupling. For example, 1/32 degrees resolution is require d to obtain a realistic separation latitude of the East Korean Warm Current (EKWC) from the Korean coast when Hellerman-Rosenstein monthly climatologi cal wind stress forcing is used. Separation of the EKWC is more realistic a t 1/8 degrees resolution when the model is forced with climatological winds formed from the ECMWF 10-m reanalysis due to strong positive wind stress c url north of the separation latitude, but at 1/8 degrees the level of baroc linic instability is insufficient to initiate upper ocean-topographical cou pling. Hence, this major topographical effect is largely missed at coarser resolution and leads to erroneous conclusions about the role of bottom topo graphy and unexplained errors in the pathways of current systems. Results f rom a 1/64 degrees simulation are similar to those at 1/32 degrees, particu larly where the EKWC separates from the Korean coast, suggesting statistica l simulation convergence for mesoscale variability has been nearly achieved at 1/32 degrees resolution. Isopycnal outcropping and associated vertical mixing provide an alternate mechanism to topographical control in developin g and maintaining a boundary current along the west coast of Japan, but are less important than baroclinic instability in driving deep mean flows.