Preliminary Study Mesoscale Eddies In The Tropical Western Pacific

The western tropical Pacific flow is complex,and it is distributed to various water masses,especially with the warm pool of this important reservoir,it is the key to regional climate change.The mesoscale eddies have a time scale of about 60 days,and the spatial scale is about 100 km.It is an important part of the multiscale system of the earth fluid,and has been studied extensively.In the tropical western Pacific Ocean,the number of eddies much smaller than those of the Kuroshio,Gulf Stream,Antarctic Circumpolar Current,and so on.Therefore,fewer studies have been done.But as a marine phenomenon of specific scale in the ocean,it is still necessary and valuable to study.In this paper,the following three parts are carried out on the meso scale eddy activities in the tropical western pacific.The first part,we statistical analysis the tropical western Pacific mesoscale eddy by use the Chelton data set,and discovered that the North Equatorial Countercurrent(NECC)area where the former research is less concerned(120°E~180°E,4°N~6°N)generated more eddy than the area of Subtropical Countercurrent where we studies a lot(120°E~180°E,15°N~17°N).And its eddy radius,amplitude,life cycle and nonlinear strength is greater.Moreover,in NECC zone,eddy moves farther,and the eddy moves obeys the gamma distribution.Eddies tend to move southward in areas close to the western boundary,while eddies in the east areas is easier to move northward.The number of eddies in this area has obvious seasonal variation,which is mainly affected by shear strength of flow field.At the same time,ENSO will affect the vortex formation in the area,and the mechanism of the effect needs further study.The second part of the eddy moving model we established is a tropical western Pacific Ocean,the initial position of the model variables,life cycle,speed is generated by computer as random number according to statistic results.The trajectories of vortices can be generated by continuously iteration.We validate the simulation result of this data set,and verify that the eddy movement model can simulate the shape of eddy moving track and reflect the moving characteristics of eddy statistically.In the third part,we study the eddy recognition method based on Lagrangian viewpoint.AVISO and OFES data were used to calculate the Lyapunov Exponent(FTLE)of the tropical western Pacific.By use of the geostrophic flow data from AVISO,we calculated the tropical Pacific Northwest backwards and forwards FTLE.We confirmed the Lyapunov exponent field ridge is the boundary of fluid transport,for example,the mesoscale eddy transport.We found four action cases of water transport of eddy: embroil,roll out,barrier,carrying.We also use the Lagrangian Averaged Vorticity Deviation(LAVD)method to visualize the separation and fusion process of two eddy in the Pacific.