Methods for studying oceanic circulation from hydrographic data are reviewed in the context of their applications in the South China Sea. These methods can be classified into three types according to their different dynamics as follows: (1) descriptive methods, (2) diagnostic methods without surface and bottom forcing, and (3) diagnostic methods with the above boundary forcing. The paper discusses the progress made in the above methods together with the advancement of study in the South China Sea circulation.
Circulations on isopycnals (σθ) 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 Ku-roshio 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 25.8σθ.The current vectors of STCC on isopycnals are
In this study, we used the Navy’s Generalized Digital Environmental Model (GDEM) climatological temperature and salinity data on a 0.5°×0.5° grid to investigate the seasonal variabilities of the southwest Philippines Sea (0.5°–9°N, 123.5°–136.5°) thermohaline structure and circulation. The GDEM for the area was built up on historical (1930–1997) temperature and salinity profiles. A three-dimensional estimate of the absolute geostrophic velocity field on isopycnal surface was obtained from the GDEM temperature and salinity fields using the P-vector method. The seasonal variabilities of the thermohaline structure and currents (obtained from the inverse method) such as the Mindanao Current, Mindanao Undercurrent, North Equatorial Counter Current, New Guinea Coastal Undercurrent, and dual-eddies (cyclinic Mindanao Eddy and anticyclonic Halmahera Eddy) are identified.
