JES Current Systems

Most of the nearly homogeneous water in the deep part of the basin is called the Japan Sea Proper Water (Moriyasu, 1972) and is of low temperature and low salinity. Above the Proper Water, the TWC, dominating the surface layer, flows from the East China Sea through the Tsushima/Korean Strait and carries warm water from the south. The LCC flows in the JES from the Okhotsk Sea through the Tatar Strait, carries cold fresh water from the north, and becomes the North Korean Cold Current (NKCC) after reaching the North Korean coast (Yoon, 1982). Both currents turn eastward to flow roughly along 40N latitude, forming the SPF between the Tsushma Warm Water and the cold and fresh water from the north (Fig. 2).

Uda (1934) was the first one to sketch the JES general circulation from limited observational data. The TWC separates north of 35N into two branches into a western and an eastern channel (Kawabe, 1982a,b; Hase et al., 1999) and flows through the western channel, called the East Korea Warm Current (EKWC), and closely follows the Korean coast until it separates near 37N into two branches. The eastern branch follows the SPF to the western coast of Sapporo Island, and the western branch moves northward and forms a cyclonic eddy at the Eastern Korean Bay (EKB). It flows through the eastern channel which closely follows the Japanese Coast, called the Nearshore Branch (NB) by Yoon (1982a). More accurately, we call it the Japan Nearshore Branch (JNB). The JNB is usually weaker than the EKWC. The strength of the Tsushima Current at both channels reduces with depth.

The NKCC meets the EKWC at about 38N with some seasonal meridional migration. After separation from the coast, the NKCC and the EKWC converge and form a strong front that stretches in a west-east direction across the basin. The NKCC makes a cyclonic recirculation gyre in the north but most of the EKWC flows out through the outlets. The formation of NKCC and separation of EKWC are due to local forcing by wind and buoyancy flux (Seung, 1992). Large meanders develop along the front and are associated with warm and cold eddies. Readers may find qualitative depiction from a textbook written by Tomczak and Godfrey (1994).

Chu et al. (1999b) identified major features of the three-dimensional circulation and the volume transport from the Navy's 0.50.5 global monthly climatological temperature and salinity data set using the P-vector method (Chu, 1995; Chu et al., 1998b). The transport pattern is largely determined by the upper layer circulation and characterized by a large-scale cyclonic recirculation gyre, in which the EKWC and the JNB take part, as the inflow-outflow system, and the NKCC in the North. At a few hundred kilometers off the separation area, the EKWC makes an anticyclonic gyre. The gyre becomes stronger as the EKWC develops. On the other hand, the northern cyclonic gyre is very deep and is most significantly in the winter strengthened by the wind and buoyancy flux. The gyre, or the southward coastal current related to it, is deep enough to intrude southward beneath the EKWC most of the time. Seung also confirmed the summertime presence of counter-current beneath the JNB. North of the SPF there exists a cyclonic gyre in the JB usually called the JB gyre.