The origin of the Tsushima Warm Current (referred to as TWC) was inves
tigated by surface drifter experiments and conductivity, temperature,
and depth (CTD) surveys in the northeastern East China Sea (ECS) at th
ree different times: July 1991, and April and November 1992. Trajector
ies of 10 satellite-tracked drifters provide direct information for th
e first time on the surface how patterns in each season, and CTD obser
vations allow identification of warm and saline TWC waters. The result
s of the experiments argue against two historical concepts of TWC orig
ins, i.e., (1) a northward flow transporting warm and saline water thr
ough the deep trough southwest of Kyushu toward the Korea Strait after
separation from the Kuroshio and (2) a northeastward continuation of
the Taiwan Current (TC) on the shelf of ECS after passing through the
Taiwan Strait. A persistent northward current was found to exist both
on the shelf west of the trough and on the western flank of the trough
. The northward flow seems to bifurcate around the northwestern corner
of the trough, splitting into a northward continuing flow on the shel
f of 100-150 m and an eastward flow along the northern wall of the tro
ugh. The northward flow on the shelf, which might be the shore fringe
of the Kuroshio, corresponds to the origin of TWC entering the Korea S
trait. The eastward flow on the northern slope turned back to the sout
h along the west coast of Kyushu and eventually joined the Kuroshio. T
his structure was accompanied by an anticyclonic eddy in the northern
trough. The second concept, that of TWC originating from TC, contradic
ts the observed differences in physical properties between TWC and TC
waters. The saline water in the Taiwan Strait flows out intermittently
only during late winter-early spring, and its salinity during other s
easons is lower than that of the TWC water in the Korea Strait. Experi
ments also indicated a seasonal shift of drifter paths in the northeas
tern ECS and coexistence of cyclonic and anticyclonic eddies in the tr
ough during the cold season.