| Ocean mesoscale eddies contain abundant energy,which can reach more than 80%of the total kinetic energy of the ocean circulation,and play an important role in the transport of ocean water,energy and nutrients.The eddy edges are rich in frontal processes,which can cause sub-mesoscale processes and strong vertical motion,and play an important role in the vertical exchange of ocean energy and materials and marine ecological processes.The study of the spatial and temporal distribution characteristics and dynamical mechanisms of eddy fronts is an important scientific issue in marine science,but due to the difficulty of obtaining relevant field data,the study of the spatial and temporal distribution characteristics and dynamical mechanisms of eddy fronts still lacks in-depth understanding.The existence of abundant mesoscale eddies in the sea east of Taiwan is an ideal place to study this scientific problem.In this paper,based on CMEMS temperature and salt data,ECMWF sea surface 10 m reanalysis wind field data and Argo buoy data,combined with dynamical diagnosis,a statistical study on the process of eddy fronts east of Taiwan is conducted to investigate in depth the spatial and temporal distribution characteristics of eddy fronts and clarify their dynamical mechanisms,which are of scientific significance to reveal the physical processes such as oceanic material and energy exchange mechanisms.The results of this study are as follows.(1)There are seasonal changes in SST,wind field and temperature fronts in the study area.the SST is higher in August and covers a wider area,while it is smaller in February.The northeast monsoon blows in winter,and the wind speed gradually increases from north to south,bringing low temperature seawater,which is conducive to the formation of temperature fronts.The southeast monsoon blows in summer,bringing high temperature seawater,which is not conducive to the formation of temperature fronts.Spring and autumn is the monsoon transition period.The surface temperature front is stronger in winter and spring,and weaker in summer and autumn.The frontal area gradually shrinks to the north as the SST rises and gradually expands to the north as the SST falls.(2)Based on the vector identification algorithm of vortices,the average radius of vortices in the study area is about 53 km,and the range is 43-69 km.the probability of occurrence is about 9.1%,and the range is 6%-17%.The probability of occurrence of vortices is smaller in winter and spring,and larger in summer and autumn.the probability of occurrence of vortices increases from February to May and the distribution range expands from month to month.the probability of occurrence of vortices and the distribution range of vortices decrease from June to January.The spatial occurrence of the eddy is skewed to the west of the study area.The spatial distribution of synthetic vortices is normalized to the vortices,and the SST and frontal intensity of synthetic vortices decrease from south to north.The positive eddy is centered on the low temperature and increases in all directions.The negative eddy is centered on high temperature and decreases in all directions.The frontal process(SST gradient)and frontal intensity in the south of the eddy are mainly provided by the positive eddy,while the north is mainly provided by the negative eddy.(3)The spatial and temporal distribution characteristics of the eddy fronts are obtained by combining the eddy and temperature front distribution characteristics.From the statistical results of eddy fronts,it can be found that the number of cyclonic and anticyclonic eddy fronts has the same trend in the monthly average distribution,and the probability of eddy fronts decreases month by month from April to August and increases month by month from September to April,but there is no obvious interannual variation.The absolute and relative probabilities of eddy fronts are larger and more widely distributed in winter and spring.The fall season is the second.In summer,the probability is smaller and the distribution is smaller.Comparing the variation characteristics of different vorticity fronts,we can see that there are more cyclonic fronts than anticyclonic fronts,and cyclonic fronts mainly exist in the western part of the study area,while anticyclonic fronts mainly appear in the North and Northwest part.Further analysis of the kinetic energy of eddy fronts shows that the kinetic energy of anticyclonic fronts is greater than that of cyclones,and there is an obvious interdecadal variation between the two,with 5 years as a cycle.The frontal kinetic energy is greater than the eddy kinetic energy,when the frontal kinetic energy is enhanced,the eddy kinetic energy is also enhanced,so the frontal kinetic energy can strengthen the eddy kinetic energy.(4)By analyzing the Argo buoy data near the eddy front,we can see that the mixed layer is deeper in winter and shallower in summer,and the disturbance occurs in the mixed layer and leap layer of temperature,salt and density near the front,and the depth and change amplitude of the disturbance are related to the distance of the buoy from the front and the intensity of the front.Analysis of the eddy front dynamics mechanism shows that the Rossby number of the eddy southern front is larger and the anisotropy is smaller,which indicates the existence of non-geostrophic process of the eddy front,while the stronger frontal strength,horizontal flow shear,horizontal buoyancy gradient and OW parameters,all indicate the existence of the eddy frontal process.The Ertel potential eddy of the eddy front is negative and there exists a strong oblique compressibility,where the transition angle is between negative 80°-90°,which is favorable to the frontal symmetric instability mechanism.In winter and spring,the absolute value of wind stress curl and wind speed are larger,which can increase the EBF on one side of the eddy and enhance the frontogenesis process and symmetrical instability,thereby increasing the probability of the appearance of the eddy front in winter and spring. |
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