Interannual variations of the winter‐time outcrop area of subtropical mode water in the western north Pacific Ocean

Abstract

Seasonal and interannual variations of the SST 16–19°C zone in the western North Pacific are described. Temperatures ranging from 16 to 19°C correspond with those of the Subtropical Mode Water (SMW) first reported and named by Masuzawa (1969). In the cooling season, this zone gradually moves southward and about December crosses latitudes 35–37°N where the Kuroshio axis lies. From January to April, the zone stagnates and spreads from the Kuroshio axis to about 28°N, i.e. to a width of about 700 km at 145°E in midwinter. This stagnation and widening are a manifestation of the existence of a thick mixed layer of SMW, i.e. the formation of a large amount of SMW, which is confirmed by several examples of the subsurface temperature distribution. In the heating season, the zone migrates northward with a narrow width as a result of the warming of the surface layer through the air‐sea interface. SST maps in March, and other related data, show the large interannual variations of the zone, especially in the sea west of the Izu Ridge. © 1987 Taylor & Francis Group, LLC.