Summertime Subtropical Countercurrent on isopycnals in the western North Pacific

Circulations on isopycnals (σ_θ) in the western North Pacific were investigated by using P-vector method; the data were taken from the U.S. Navy’s climatological temperature and salinity dataset (public domain) with 1/2° ×1/2° resolution. Results not only show the main circulation systems on isopycnals in the western North Pacific such as the North Equatorial Current (NEC), Kuroshio and Kuroshio Countercurrent, but also reveal the Subtropical Countercurrent (STCC) clearly. In this note we pay attention to discussing the distribution of STCC in summer (in June). The STCC flows eastward along a winding road; on shallow isopycnals, the STCC originates from the area east of Bashi Strait at about 122.5°E; with the isopycnals increasing, the origin and flow core of STCC move to north and east, but the main part of STCC is still between 18° and 23.5°N, i.e. near the Tropic of Cancer. There exists STCC on all isopycnals between the sea surface and 25.8 σ_θ. The current vectors of STCC on isopycnals are shown for the first time, and the distribution of the potential vorticity indicates that STCC is just overlying the southern boundary of the Subtropical Mode Water (STMW).