| Based on the CTD observation data off the coast of Philippines (7.5°- 18°N, 130°E - the east coast of Philippines) in fall of 2005 from the National 863 Project, the water masses in the source region of North Pacific west boundary currents is classfied, the geostrophic flow field is calculated and the characteristics of circulation in this region is analyzed systematically, and a preliminary analysis of heat flux there was conducted.There are mainly four water masses in the upper 2000m off the coast of Philippines: the North Pacific Tropical Surface Water (NPTSW), the North Pacific Sub-surface Water (NPSSW), the North Pacific Intermediate Water (NPIW) and the Antarctic Intermediate Water (AAIW). All of them are deeper in northern part than in southern part. The NPSSW has a significant character for high salinity, with a maximum of 35.44, which is formed in the open ocean and transported by the North Equatorial Current (NEC) to the study area; The NPIW characterizes by low-salt, with the core of salinity less than 34.20, and it is the lowest salinity of middle-water masses in the world ocean, which was from the sub-Arctic region and carried by the NEC to the west boundary, then bifurcates into two branches there; The AAIW is mainly distributed in the south of 12°N, most of them are below and to the east side of the NPIW, with the core salinity between 34.4-34.5. It originates in sub-polar of the South Pacific, then crosses equator and partly flows northward along the coast, which formed the Mindanao Undercurrent (MUC) that flows into the study area.The NEC distributes between 8°-18°N, and the surface velocity is more than 30cm/s. With the northward extension, the NEC increases its depth distribution, which is the result of potential vorticity conservation. The Subtropical Countercurrent (STCC) is between 18°-20°N to the north side of the NEC, the surface velocity is about 30cm/s. The North Equatorial Countercurrent (NECC) is between 2°-8°N, the surface velocity is up to 70cm/s. After separating from the NEC, the Kuroshio Current (KC) enhances northward, the surface velocity in 18°N is greater than 81cm/s, the depth and width of it is up to 1300m and 100km separately, and there are several eddies to the right side of it. The Mindanao Current (MC) becomes intense when flows southward from 12°to 7.5°N, the surface velocity inshore at 7.5°N is greater than 190cm/s, and the width is very narrow. There is countercurrent or undercurrent below the NEC, KC and MC, and the latter two are known as the Luzon Undercurrent (LUC) and MUC. The LUC locates below the inshore side of the KC, and is about 300m under the sea surface. Its width is no more than 50km, and the maximum velocity is about 5cm/s. The MUC locates below the MC, with the depth of more than 200m, and the thickness of more than 1000m. And it is characterized by multi-core, with core velocities ranging from 5cm/s - 20cm/s. The bifurcation point of the NEC in the western boundary varies from 13°N at the surface to 18°N at 700m, and the depth-averaged position is at about 15°N. The northward shift with the increasing depth is the result of potential vorticity conservation. The volume transports of above currents are calculated, and the sketch map of the circulation off Philippines coast is drew systematically, including the NEC for 58.7Sv, the KC for 15Sv, and the MC for 27.95Sv. The results show that, the quasi-closed region reaches basic conservation of mass when choose 1500db as zero reference level. From the stratified analysis of the volume transport, it is concluded that there is an anticyclonic eddy in the southeast of the region below 500m, of which the MUC is probably the west banch.At last, direct calculation is used in the study of heat flux. As a result, the net heat transport is about 1.45×106GW outwards the region, with the same direction as the volume transport. What's more, the vertical circulation is revealed to contribute far more than the horizontal circulation to the heat transport. At the same time, the ocean is proved of losing heat to the air by the net heat flux data of the sea surface, while the air-sea heat exchange is remarkably small compared with the heat transport inside the ocean. The whole heat budget including at the surface and inside the ocean caused the sea temperature reduction, with a rate of 0.75℃per month, and the trend is corresponded with the SST change during that period. Heat transport through each section and along each current are also calculated in the study. Ultimately, a systemic heat budget structure in the source region of western boundary current system is shown as a figure. There are some features with the vertical structure: most heat is carried by the surface water, subsurface water and intermediate water, which are warmer than 5℃. When stratified in depth, the net heat transport in the referred region is almost completed in the upper 500m.
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