Oceanic surface current that flows northwards from the Philippines, along the Japanese coast, and then out into the N. Pacific. It is an example of a western boundary current: fast-flowing (up to 3 m/s), narrow (less than 80 km), and relatively deep. It is second in strength only to the Gulf Stream. The warm water transports heat polewards. The volume transport is variable but is normally about 4 × 107 m3/s.