| Meso-scale eddies in the region of Subtropical Countercurrent (STCC) in the Northwest-Pacific are active and they are important ocean processes in such area. In this study, two methods are used to investigate these eddies' characteristics. One method is analyzing the satellite altimeter data, the other is using reanalysis technology. By analyzing the satellite altimeter data, the distribution and the evolvement of the eddies are studied. To study the eddies' three-dimensional structures and their dynamics in detail, as well as their action on the Kuroshio, an ocean reanalysis system is constructed, which is based on the s-coordinate Princeton Ocean Model (POMs), and three-dimensional variational (3DVAR) ocean data assimilation. Using such reanalysis system, ten years of altimeter data, sea surface temperature data, Argo data and other tempareture and salinity profile data are reprocessed. In order to produce a better reanalysis of the ocean state, a new method of 3DVAR is designed, which is named Sequential 3DVAR (S3DVAR). This assimilation method can retrieve information from larger scale to smaller scale.Based on the analysis of the satellite altimeter data and the reanalysis of sea surface height during 1996～2005, it is suggested that there are 50～70 eddies in STCC and adjacent area yearly averaged, in which, there are more cyclonic eddies than anticyclonic eddies. The average radius of the eddies is about 170km, and the difference of sea surface heigh between the eddy's center and boundary usually ranges from 10cm to 40cm. It is revealed that there are more eddies in this area in spring and summer, while in autumn and winter their amount decreases and their intensity becomes weaker, and lifetime shorter too.Based on the reanalysis of current field, the three dimensional structures of the eddies in the area of STCC are studied in detail. When the edge of the meso-scale eddies is set as the position where the rotate velocity is 5cm/s, the anticyclonic eddies are always in the form of taper with depth between 1000m to 2000m. On the contrary, the shapes of cyclonic eddies are generally column with depth several hundred meters. The tempareture field suggests that the depth of cold core of cyclonic eddy or warm core of anticyclonic eddy is very deep, and usually several hundred meters deeper than the depth reached by the current field, while at the depth shallower than 100m, the cold core or warm core of the eddies is not evident.Most of the researches believe that baroclinic instability is the main source of the eddy kinematic energy in the area of STCC, while the impact of wind on the activity of these eddies is seldom paid attention to. In this study, some numerical experiments are carried out with NCEP and QuikSCAT wind data, and the wind curves of the two sets of data are studied. It is revealed that the seasonal variety of the meso-eddies is obviously correlated to the QuikSCAT wind curves. The result of the study of this thesis indicate that wind curves can evidentily impact on the seasonal variety of the meso-eddies in STCC. It is indicated that, when the QuikSCAT wind is used, the ability of reproduction eddies of the model can be improved.Based on the reanalysis of current field, the impact of meso-scale eddies on the flux of Kuroshio and Luzon channel is discussed. It is revealed that the action of mesoscale eddies can change the Kuroshio flux obviously, and there is no eddies enter into the South China Sea through Luzon channel.
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