Oceanic 3D vortex coreline extraction using the objective λ2 method
Vortex corelines are an important component of the oceanic mesoscale eddy structure.The extraction and visualization of the vortex corelines are of great significance for the study of the three-dimensional structure of the mesoscale eddies and the analysis of the vertical oceanic material and energy transport.Based on the objective reference frame and the λ2 criterion,this paper proposes a method to obtain the λ2 region using the objective flow field parameters;and extract its valley line as the vortex coreline.First,the optimal local reference frame is introduced;so that measurements such as velocity and velocity gradient become objective quantities that remain unchanged under the changing reference frame,which improves the reliability and practicability of marine science practice.Secondly,for the three-dimensional ocean flow field data with vertical velocity,the spatial Jacobian matrix is calculated,which shows the three-dimensional structure of the vortex core region,and realizes the improvement of ocean vortex research from two-dimensional to three-dimensional.Finally,the experimental results of the extracted vortex corelines are verified by the analysis of vortexs in the different rotation directions and the different radius of streamline seed points,which proves the effectiveness and feasibility of the objective λ2 ocean three-dimensional vortex coreline extraction method.
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