Study On The Characteristics Of Typical Oceanic Mesoscale Eddies

Mesoscale eddy is an indispensable part of ocean circulation,with a typical spatial scale of several to hundreds kilometers and a time scale ranging from weeks to months.As a connection of the large ocean currents to small scale movements,mesoscale eddy plays an important role in transportation and mixing of mass,heat,energy,nutrition,etc in the ocean.Meanwhile it also has a great impact on multi-scale ocean movements,marine ecology,atmosphere condition,and climate change.This dissertation focuses on the study of mesoscale eddies,using both Eulerian and Lagrangian methods which both have their own inherent advantages and disadvantages.The Eulerian method is effective in analyzing short-term properties of the eddies while the Lagrangian method is much more competent when it comes to the study of longexisting eddies and ocean water transportation.First,we did a statistic study of mesoscale eddies in the South China Sea(SCS)followed by a predictivity study of the SCS dipole and discussed the impact of ENSO on the SCS dipole.Then the Lagrangian nonlinear dynamical systems theory and methods are introduced which have been further applied on the detection of Agulhas rings.Unlike former studies,we found the water carried inside those long-existing Agulhas rings is actually formed largely from the Atlantic ocean water.Meanwhile our study focused on a specific long-existing Agulhas ring shows that the super coherent cores are surrounded by short-term coherent loops which can absorb incoherent water from turbulent surroundings and transform them into coherent water thus make the coherent structure to grow.We also found that the reason the Agulhas ring can stay coherent for more than a year can attribute to the shielding of the high-energetic boundary.