Closed lateral boundaries, i.e., the modeled ocean bordered by land, were defined using a free slip condition for velocity and a zero gradient condition for temperature and salinity. No advective or diffusive heat, salt or velocity fluxes occur through these boundaries.
At open boundaries, the numerical grid ends but the fluid motion is
unrestricted. Uncertainty at open boundaries makes marginal sea modeling
difficult. Three approaches, local-type, inverse-type, and nested
basin/coastal modeling, are available for determining the open boundary
condition (Chu et al., 1997). Here, we take the local-type approach, i.e., to
use the radiative boundary condition with specified volume transport. When the
water flows into the model domain, temperature and salinity at the open
boundary are likewise prescribed from the Navy's climatological data. When
water flows out of the domain, the radiation condition was applied,
where the subscript is the direction normal to the boundary.
Warm water enters the JES through the Tsushima/Korean Strait with the TWC from the East China Sea, and cold water enters the JES through the Tatar Strait with the Liman Current from the Sea of Okhotsk (Uda, 1934). The water exits the JES through the Tsugaru and Soya straits. We use a more recent estimation of the monthly mean volume transport, reported by Chu et al. (1999b), through the Tsushima/Korean Strait with the annual average of 1.3 Sv, a maximum of 2.2 Sv in October, and a minimum of 0.3 Sv in February. The total inflow transport through the Tatar and Tsushima/Korean straits should be the same as the total outflow transport through the Tsugaru and Soya straits. We assume that 75% of the total inflow transport should flow out of the JES through the Tsugaru Strait, and 25% through the Soya Strait. The monthly volume transports at open boundaries are listed in Table 1.
Table: Monthly variation of volume transport (Sv) at the lateral open
boundaries. The positive/negative values mean inflow/outflow.