Diagnoses of simulated water-mass subduction/formation/transformation in the Japan/East Sea (JES)

The presence of simulated dense surface water (>σθ=26.8) in the northern JES is due to the effects of synoptic events during winter months when large heat loss and strong wind stress associated with cold-air outbreaks and extratropical cyclones occur. The convection magnitudes as a result of air-sea interaction are 3.0, 4.0, and 6.0 Sv for mont, empm, and syn, respectively. A net flux of mass from the interior to the mixed layer (entrainment) occurs in the density range between σθ=24.0 and σθ=26.2 for both empm (3.5 Sv) and syn (3.0 Sv), while it occurs in the density range between σθ=24.0 and σθ=25.8 for mont (2.8 Sv). The diffusive fluxes across the winter mixed layer base are about 0.8, 1.0, and 1.4 Sv for mont, empm, and syn, respectively. An undiagnosed eddy-induced turbulent mixing (the residual of the balance after removing discretization error) for syn is almost twice that for the other two cases (mont and empm). These results indicate that without synoptic atmospheric forcing, the diagnostics using the numerical circulation model may significantly underestimate buoyancy loss at the surface, and, hence, water-mass formation, as well as mixing and spreading of the formed water mass.