A new 3DVAR-based Ocean Variational Analysis System (OVALS) is developed. OVALS is capable of assimilating in situ sea water temperature and salinity observations and satellite altimetry data. As a component of OVALS, a new variational scheme is proposed to assimilate the sea surface height data. This scheme considers both the vertical correlation of background errors and the nonlinear temperature-salinity relationship which is derived from the generalization of the linear balance constraints to the nonlinear in the 3DVAR. By this scheme, the model temperature and salinity fields are directly adjusted from the altimetry data. Additionally, OVALS can assimilate the temperature and salinity profiles from the ARGO floats which have been implemented in recent years and some temperature and salinity data such as from expendable bathythermograph, moored ocean buoys, etc. A 21-year assimilation experiment is carried out by using OVALS and the Tropical Pacific circulation model. The results show that the assimilation system may effectively improve the estimations of temperature and salinity by assimilating all kinds of observations. Moreover, the root mean square errors of temperature and salinity in the upper depth less than 420 m reach 0.63℃ and 0.34 psu. Keywords: data assimilation, 3DVAR, sea surface height, ARGO floats.With the successful development of ocean buoys technique in the 1990s, the ARGO plan was proposed by the international group in 1998 and implemented in 1999. Up to now, more than 1800 ARGO floats are now in operation and delivering real-time temperature and salinity profile observations over the world oceans. By the end of 2005, ARGO will expect to provide more than 100000 temperature and salinity profiles which have a depth range of 0 m to 2000 m [1] . Apart from the ARGO plan, the GODAE high-resolution sea surface temperature pilot project (GHRSST-PP) is beginning to implement to provide high resolution in the time of 6 h and in the space of 10 km [2] sea surface temperature observation with global coverage for the operational oceanography, climate study and prediction. Except the above two new observation systems, as a successor of successful implementation of Topex/Poseidon altimeter satellite in the 1990s, the Jason-1 Mission was successfully launched in December, 2001. This observation system can provide

[1] A three-dimensional absolute velocity field on the isopycnal surface in the northwest Pacific subtropical region in the summer is calculated from the Navy's Generalized Digital Environmental Model (GDEM) climatological temperature and salinity data on a 0.5°Â 0.5°grid using the P-vector method. GDEM for the area was built from historical temperature and salinity profiles. The basic current system, consisting of North Equatorial Current, Kuroshio and its recirculation, Subtropical Countercurrent (STCC), is identified. STCC occurs from the surface to the level of s q = 25.8 between 18°N and 23.5°N, with a maximum velocity around 0.1 m/s. At s q = 23.5, STCC originates east of Luzon Strait at around 122.5°E and meanders eastward. As s q increases, its origin shifts toward northeast. Comparison between velocity and potential vorticity fields leads to the conclusion that the STCC core is above the southern boundary of the subtropical mode water.