Gordon, A.L., and C.F. Giulivi, Pacific decadal oscillation and sea level in the Japan/East Sea, Deep-Sea Research I, 51, 653-663, 2004. [ Abstract ]
Gordon, A.L., C.F. Giulivi, C.M. Lee, H.H. Furey, A. Bower, and L. Talley, Japan/East Sea intrathermocline eddies, Journal of Physical Oceanography, 32, 1960-1974, 2002. [ Abstract ]
Ou, H.W., A model of buoyant throughflow: With application to branching of the Tsushima Current, Journal of Physical Oceanography, 31, 115-126, 2001. [ Abstract ]
Ou, H.W., On the cooling of a buoyant boundary current, Deep-Sea Research II, 52, 1662-1670, 2005. [ Abstract ]
Ou, H.W., and A.L. Gordon, Subduction along a midocean front and the generation of intrathermocline eddies: A theoretical study, Journal of Physical Oceanography, 32, 1975-1986, 2002. [ Abstract ]
Gordon et al., 2004
Satellite altimetric data from September 1992 to January 2002 and hydrographic data from 1927 to 1999 reveal the presence of low-frequency variability of sea surface height (SSH) within the Japan/East Sea (JES). SSH interannual variability amounting to approximately 15 cm is in phase with the Pacific Decadal Oscillation (PDO), with higher SSH, warmer, fresher surface (upper 200 dbar) layer during negative phases of the PDO; and lower SSH, cooler, saltier surface layer during a positive PDO. The JES SSH correlation with PDO appears to be related to changes in the geostrophic transport of the Kuroshio, which is weaker during a negative PDO (stronger during positive PDO). The transport of the Tsushima Current, which feeds the JES, is reported to be out of phase with the Kuroshio transport, thus delivering more buoyant subtropical water to the JES when the Kuroshio is weak. Part of the JES baroclinic PDO-related variability may also be due to changes in the freshwater inflow from the East China Sea, which is closely associated with the discharge of the Yangtze River.
Gordon et al., 2002
Intrathermocline eddies (ITE) with diameters of 100 km and of thickness greater than 100 m are observed within each of the three quasi-stationary meanders of the Tsushima Current of the Japan/East Sea. Within the ITE homogenous, anticyclonic flowing core, the temperature is near 10°C with a salinity of 34.12 psu. Because of compensatory baroclinicity of the upper and lower boundaries of the ITE core, the ITE has minor sea level expression. The ITE core displays positive oxygen and negative salinity anomalies in comparison to the surrounding thermocline water, indicative of formation from winter mixed layer water along the southern side of the Japan/East Sea subpolar front. The winter mixing layer is then overridden, or slips below, the regional upper thermocline stratification with its characteristic salinity maximum layer. The winter mixed layer off the coast of Korea closely matches the ITE core characteristics, and is considered as a potential source region. Other sources may be present along the southern boundary of the subpolar front, including a frequently observed warm eddy over the western side of Yamato Rise.
A reduced-gravity model is used here to investigate the dynamics of a buoyant flow through a strait driven by pressure difference of the adjoining basins. Assuming the flow to be hydraulically controlled so that the transport is maximized, flow structures in the upstream basin, during its transit through the strait and along the downstream coast, are determined.
It is found in particular that the combined effect of friction exerted by the sill and stretching of the buoyant layer as it exits the strait may cause the downstream flow to exhibit two velocity maximaalong the layer outcrop and the coastal boundary. When applied to the Tsushima Current of the Japan/East Sea, the required conditions for branching are amply satisfied, the model thus provides a plausible explanation of this observed feature. In addition, a favorable comparison between predicted and observed transports supports the hydraulic control of the flow.
Through a steady-state reduced-gravity model, we examine the downstream evolution of a buoyant boundary current as it is subjected to surface cooling. It is found that the adverse pressure gradient associated with the diminishing buoyancy is countered by falling pressure head, so the overall strength of the currentas measured by the (transport-weighted) mean square velocityremains unchanged. This constancy also applies to the cross-stream difference of the square velocity because of the vorticity constraint, which leads to the general deduction that the net current shear is enhanced regardless of its upstream sign. As a consequence, if the upstream flow contains near-shore and offshore branches that are comparable in strength, this parity would persist downstream; but if the near-shore branch is weaker to begin with, it may be stagnated by cooling, with the ensuing generation of anti-cyclonic eddies. On account of the geostrophic balance, the buoyant layer narrows as the square root of the buoyancythe same rate as the falling pressure head, but more rapid than that of the local deformation radius. Some of the model predictions are compared with observations from the Tsushima Current in the Japan/East Sea.
Ou and Gordon, 2002
Through an idealized model, the authors consider the dynamics of subduction along a midocean front and its linkage to the intrathermocline eddies (ITEs). The subduction is necessitated by advective-diffusive balance of potential vorticity (PV), with its flux mainly a function of the mixed layer depth over the normal range of the horizontal diffusivity. The mismatch of PV impedes the entry of the subducted water into the interior, resulting in an excess flux that peaks at some intermediate mixed layer depth. This mismatch also causes the generation of anticyclonic ITEs, whose radius contains no lower bound, and a maximum limited by the entrainment rate. Through entrainment cooling, ITEs may leave their imprints in the surface temperature, giving rise to a meandering appearance of the front, even in the absence of instability.