Three-dimensional mesoscale eddy identification and tracking algorithm based on pressure anomalies Liming

The Kuroshio Extension(KE)is one of the most eddy-energetic regions in the global ocean.However,most mesoscale eddy studies in the region are focused on surface eddies and the structure and characteristics of three-dimensional(3-D)eddies require additional research.In this study,we proposed a 3-D eddy identification and tracking algorithm based on pressure anomalies,similar to sea level anomalies(SLAs)for surface eddy identification.We applied this scheme to a 5-year(2008-2012)high-resolution numerical product to develop a 3-D eddy dataset in the KE.The reliability of the numerical product was verified by the 5-year temperature/salinity hydrological characteristics and surface eddy distribution.According to the 3-D eddy tracking dataset,the number of eddies decreased dramatically as the eddy existence-time increased and more anticyclonic eddies(AEs)had an existence-time longer than 1 week than cyclonic eddies(CEs).We presented daily variations in the 3-D structure of two 3-D eddy-tracking trajectories that exhibit a certain jump in depth and a shift toward the west and equator.In addition to the bowl,lens,and cone eddies that have been discovered by previous researchers,we found that there is a cylindrical eddy,and its eddy radii are almost consistent across all layers.CEs cause significant negative temperature anomalies,“negative-positive”salinity anomalies,and sinking current fields in the KE region,while AEs cause positive temperature anomalies,“positive-negative”salinity anomalies,and upward current fields.The four types of eddies have different effects on the temperature/salinity anomalies and current field distribution which are related to their structure.

Lagrangian eddies in the Northwestern Pacifi c Ocean

The Lagrangian eddies in the western Pacifi c Ocean are identifi ed and analysed based on Maps of Sea Level Anomaly(MSLA)data from 1998 to 2018.By calculating the Lagrangian eddy advected by the AVISO velocity fi eld,we analyzed the variations in Lagrangian eddies and the average transport eff ects on diff erent time scales.By introducing the Niño coeffi cient,the lag response of the Lagrangian eddy to El Niño is found.These data are helpful to further explore the role of mesoscale eddies in ocean energy transfer.Through normalized chlorophyll data,we observed chlorophyll aggregation and hole eff ects caused by Lagrangian eddies.These fi ndings demonstrate the important role of Lagrangian eddies in material transport.The transportation volume of the Lagrangian eddy is calculated quantitatively,and several major transport routes have been identifi ed,which helps us to more accurately and objectively estimate the transport capacity of Lagrangian eddies in the western Pacifi c Ocean.

Transfer function-based 2D/3D interactive spatiotemporal visualizations of mesoscale eddies

In this paper,we present a transfer function-based approach to developing an interactive visualization algorithm for ocean mesoscale eddies.Spatiotemporal coherence and viewport coherence are achieved.Evenly spaced streamlines are only integrated for visible portions of the datasets that maintain a relatively stable visual pattern resolution.The interactive transfer function is introduced to extract 2D and 3D eddy features,such as the Okubo-Weiss parameter,from background ocean currents,and a highly efficient GPU-based framework with an outputsensitive performance is utilized.Using the high-resolution 2D/3D ocean current datasets Maps of Sea Level Anomalies(MSLA)and Hybrid Coordinate Ocean Model(HYCOM),the feasibility and efficiency of our framework are demonstrated.

i4Ocean: transfer function-based interactive visualization of ocean temperature and salinity volume data

In this paper,we present a novel ocean visualization framework,which focuses on analyzing multidimensional and spatiotemporal ocean data.GPU-based visualization methods are explored to effectively visualize ocean data.An improved ray casting algorithm for heterogeneous multisection ocean volume data is presented.A two-layer spherical shell is taken as the ocean data proxy geometry,which enables oceanographers to obtain a real geographic background based on global terrain.An efficient ray sampling technique including an adaptive sampling technique and a preintegrated transfer function is proposed to achieve high-effectiveness and high-efficiency rendering.Moreover,an interactive transfer function is also designed to analyze the 3D structure of ocean temperature and salinity anomaly phenomena.Based on the framework,an integrated visualization system called i4Ocean is created.The visualization of ocean temperature and salinity anomalies extracted interactively by the transfer function is demonstrated.

The geometry of mesoscale eddies in the South China Sea: characteristics and implications

The symmetrical circular shape of mesoscale eddies has been widely used in their scientific researches.Recently,an elliptical average eddy shape has been confirmed for eddies in the global ocean using multi-satellite altimeter data.As a regional extension of a previous study on the geometry of global eddies,a mean eddy shape in the South China Sea(SCS)has been derived by averaging a large number of orientational eddy boundaries.The mean shape is approximately a mathematic ellipse with a semimajor axis of 101.3 km and a semiminor axis of 61.3 km.Its size is larger than the global one.The principal eddy orientation in the SCS is 74°/254°(nearly northeast-southwest),different from that of eddies in the global ocean(171°/351°,nearly east–west).Composite analyses of chlorophyll(CHL)concentrations and sea surface temperature anomalies(SSTA)indicate a dipole structure for circular eddies in the non-rotated coordinate system.While a monopole structure for elliptical eddies in the eddy-centric coordinate system is obtained.The results demonstrate that the elliptical shape of eddies affects oceanographical variables.The findings provide a new approach for exploring the role of air–sea interactions on oceanic eddies.