A Dynamic Tracking Dataset With Merging And Splitting Events For Mesoscale Eddies In The Ocean

Eddies are ubiquitous in the ocean,and they move from one place to another.Eddies in the ocean can cause large-scale transports of heat,salt,and other tracers by trapping these passive tracers inside the eddies.Such transports may have important impacts on the environment and climate of the ocean.There were some problems with the previous eddy identification and tracking methods.In previous methods,multi-core eddies were identified to be one eddy,which should be divided into mononuclear eddies.Besides,the eddy dynamic evolution(merging,splitting,etc.)were ignored in previous eddy tracking part.So it is important and necessary to develop a new mononuclear eddy identification and a new dynamic tracking model and dataset for mesoscale eddies in the ocean.In this paper,a new watershed strategy for oceanic mesoscale eddy splitting is proposed to segment the ocean mesoscale multi-core eddies,which solves the multi-core eddy identification problem effectively.The segmentation strategy can accurately divides multi-core eddy into mononuclear eddies.The Genealogical Evolution Model(GEM)is an efficient logical model used to track dynamic evolution of mesoscale eddies in the ocean.It can distinguish between different dynamic processes(e.g.,merging and splitting)within a dynamic evolution pattern,which is difficult to accomplish using other tracking methods.To this end,the GEM first uses a two-dimensional(2-D)similarity vector(i.e.,a pair of ratios of overlap area between two eddies to the area of each eddy)rather than a scalar to measure the similarity between eddies,which effectively solves the missing eddy problem(temporarily lost eddy in tracking).Second,for tracking when an eddy splits,the GEM uses both parent(the original eddy)and child(eddy split from parent)and the dynamic processes are described as the birth and death of different generations.Additionally,a new look ahead approach with selection rules effectively simplifies computation and recording.All of the computational steps are linear and do not include iteration.Given the pixel number of the target region L,the maximum number of eddies M,the number N of look-ahead time steps,and the total number of time steps T,the total computer time is O(LM(N+1)T).The tracking of each eddy is very smooth because we require that the snapshots of each eddy on adjacent days overlap one another.The tracking dataset presented here records the dynamic evolution(e.g.birth,death,living,missing,splitting,and merging)of global mesoscale ocean eddies identified from satellite altimetry data over a period of 1993-2016 using our new open source Genealogical Evolution Model(GEM).It contains?1,089,092 eddies features(amplitudes,areas,lifetime,etc.)and?351,732 eddy trajectories with lifetime longer than 28 days.All the merging and splitting processes are recorded during the entire life cycle of each eddy.It provides an important foundation for studying the basic properties of ocean mesoscale eddies and the dynamics of eddies.Statistical analysis of the eddy data products revealed that the average life cycle of the eddy is about 97 days,and the maximum life cycle is 2455 days(anticyclonic eddy),which lasts for 6 years;the average amplitude is 17cm,and the maximum amplitude exceeds 2m.The average radius is about 100km.Eddies mainly exist in the region of Kuroshio Extension,Warm Current of Mexico Gulf,the Atlantic Current,the Brazil Current and other relatively strong currents.Meanwhile,there is no significant difference between the distribution of cyclonic eddy and anticyclonic eddy.Most of the eddies propagated westward,with most cyclonic eddies moving toward the poles,and anti-cyclonic eddies to the equator.Eddies prefer to be generated in the eastern boundary of the ocean,while demise in the west boundary.As the eddy life cycle and propagation distance increases,eddy number decreases rapidly.Compared with the anticyclones,cyclonic eddy propagates longer distances,but the life cycle is shorter.Eddy interacts with other eddies,such as merging and splitting.Most of the events mainly occur in the vicinity of strong ocean currents where there are more eddies respectively.Besides,as the eddy life cycle increases,the frequency of splitting and merging increases almost linearly.Long-lived eddy prefers to be anti-cyclone,indicating that cyclones are more likely to dissipate.In addition,the eddy number changes seasonally,and the global eddy number reaches its maximum in December and January.