Analyses Of Mesoscale Eddies In North Pacific

The North Pacific Ocean lies in east of the Chinese continent, which has a complicated circulation system. Mesoscale features are active in this area. In this thesis, mesoscale eddies are tracked with an automated eddy identified procedure in North Pacific area(120°E～100°W，10°N～60°N) within nineteen years(1993~2011), and spatial-temporal features and movements of these eddies are analyzed.There are about1800eddies emerge in North Pacific every year, with960cyclones and840anti-cyclones. The most clearly defined regions of frequent eddy formation include the coast of California and Japan, the Kuroshio extension and southern part of the Subtropical Countercurrent area. The geographical distribution of polarity has a correlation with currents and the latitude of35°N can be its dividing line. Mesoscale variability is predominantly cyclonic in south of the line and anti-cyclonic in north of it. The radius of eddies has a maximum of about100kilometers and the average radius decreases with latitude. Anti-cyclones have larger radius than cyclones for about5km. The Kuroshio extension area has larger eddy amplitudes than other ocean areas, followed by the region of Subtropical Countercurrent and Aleutian ocean currents. The number of eddies decrease deeply with lifetime, and eddies with lifetime shorter than10weeks counts for about60%of all eddies. Anti-cyclones are more preferred on cyclones in long lifetime eddies. Overall, the average amplitudes, radius, lifetimes and propagation distance of anti-cyclones are longer than cyclones and the average radius and amplitudes of eddies with long lifetimes are usually larger than eddies with short lifetimes.The number of stationary eddies (with meridional propagation distance smaller than1°), southward transform eddies, northward transform eddies has proportion of9:3:2, and the number of westward transform eddies, stationary eddies(with zonal propagation distance smaller than1°), eastward transform eddies has proportion of9:3:1. Cyclones and anticyclones have distinct preferences for poleward and equatorwad deflection, respectively. The propagation distance of eddies has a maximum of about300kilometers and half of eddies have propagation distance between150km and550km.There is an obvious seasonal change in emerge of mesoscale eddies. It is revealed that there are more eddies emerge in spring and less eddies emerge in autumn, about20%less than spring.Mesoscale eddies results and Argo floats put in North Pacific are combined to study the vertical temperature structure of eddies in this area. It is revealed that eddies have ‘core’ structure. The temperature anomaly caused by eddies increases at first and decreases with depth.50m~300m is the main depth affected by eddies and the influence can extend to depth of800m. The cold core of cyclones lies in the depth of150m and the largest temperature anomaly is about-1.3°C while the warm core of anticyclones lies in depth of120m and the largest temperature anomaly can reach1.5°C.To reveal the difference of eddy structures in different locations, the region of the Subtropical Countercurrent, the Kuroshio extension, the Oyashio Current and east coast of North Pacific are chosen to study their eddy structure. The results show that cyclones and anticyclones have similar structure in the same area but the structure of eddies in different regions distinct from each other. Especially eddies in the Kuroshio extension area have large difference in vertical structure with other regions. The vertical temperature anomaly of eddies in this area is larger than other areas and the depth of cores is deeper than other regions. Furthermore, there is large temperature anomaly in depth from100m to600m on eddies in this area.