Study On The Distribution Of Eddy Characteristics In The Indian Ocean Sector Of The Southern Ocean Based On Satellite Remote Sensing Observations

The Southern Ocean contains the world’s largest current and the most dynamic eddy field.Significant eddy activity affects the momentum balance and meridional overturning circulation of the Antarctic Circumpolar Current(ACC)in this ocean.The subantarctic front(SAF),polar front(PF),Southern Antarctic circumpolar current front(SACCF),and Southern boundary of the ACC(SBdy)are distributed along the ACC flow axis from north to south.These fronts are thought to have strong interactions with eddies.In the Indian Ocean sector of the Southern Ocean,there are special topography such as the Kerguelen Plateau,the Balleny Fracture Zone,which affect the intensity and characteristic distribution of the eddies.At the same time,the convergent flow of the ACC and the Agulhas Return Current in the Kerguelen Plateau area further strengthens the downstream oblique pressure shear intensity,leading to a significant enhancement of the eddy energy.Based on the satellite remote sensing data from 2005-2019,this paper provides statistics on the eddy characteristics in the Indian Ocean sector of the Southern Ocean,analyzes the distribution of eddy generation sites and the movement status of cross-frontal eddies,and further analyzes the internal hydrological distribution characteristics of eddies by combining with the Argo profile data.The results of the study in the Kerguelen plateau area show that the life cycle of the eddies in the area is mostly within 40 d(76.76%)and the average radius is mostly between 30-100 km(94.79%);the average radius is positively correlated with the average amplitude(correlation coefficient R=0.53);the larger the life cycle of the eddies,the larger the average propagation distance.The number of eddies is mainly contributed by short-lived eddies(<80 d),and the annual mean eddy kinetic energy anomaly tends to decrease in the late 2010 s.The high percentage of short-lived(<80 d)eddies is concentrated downstream of the Kerguelen Plateau,and the eddies gradually move from the frontal area between SAF and SBdy to the north of SAF as the life span gets longer.The longer the life cycle,the less the generation of eddies close to the land area(southern part of the South African continent and the Kerguelen Plateau region).The larger eddy radius(>50 km)is concentrated north of SAF,and the larger eddy amplitude(>15 cm)is concentrated in the Agulhas Return Current.There are differences in the direction of eddy movement.The number of eddies moving eastward between fronts accounts for 70.69% of the total number of eddies between fronts.Among the inter-frontal eddies,warm eddies move to high latitudes and cold eddies move to low latitudes,and most of them have the ability to carry water masses.The results of the study in the southern Australian waters show that the life cycle of eddies in this area is mostly within 40 d(76.14%),and the average radius is mostly between 30 and 100 km(93.34%);the larger the life cycle of eddies,the larger the average propagation distance.The number of eddies is mainly contributed by shortlived eddies(<80 d).The high values of eddy generation sites with short life cycle(<80 d)are concentrated in the Balleny Fracture Zone and its downstream,and Australia’s Eastern Sea Region.The eddy generation sites gradually move from the frontal area between SAF and SBdy to the north of SAF as the life span gets longer.The larger values of eddy mean radius(>50 km)are concentrated in the sea north of SAF,especially in eastern and southern Australia,and the larger values of eddy mean amplitude(>15 cm)are concentrated in the sea of SAF in eastern Australia and downstream of the Balleny Fracture Zone.The longer spatial distribution range of the anticyclonic eddy life cycle extends into the eastern Australian waters compared to the cyclonic eddy.There are also differences in the direction of eddy movement,with the northern SAF and southern SBdy eddies moving mainly to the west,and only 36.09%of the eddies moving eastward in the northern SAF and 32.88% in the southern SBdy,while the number of eddies moving eastward between fronts accounts for 64.60% of the total number of eddies between fronts.The number of cross-frontal eddies,warm eddies to high latitudes,cold eddies to low latitudes,cross-frontal eddies are mainly concentrated in the Balleny Fracture Zone,where the number of eddies across the SAF front is the largest,most of which have the ability to carry water masses to move.The statistical analysis of the eddies downstream of the special topography(Kerguelen Plateau,Balleny Fracture Zone)shows that the radius and amplitude of the eddies are small compared with the nature of the eddies in the whole area,and the areas with large eddies are concentrated in the northern part of the SAF.The analysis of the statistical results of the eddy propagation velocity downstream of the two special terrains reveals that the eddy life cycle and propagation velocity in the selected areas are consistent with the overall eddy between the fronts.There is no significant difference in the eddy propagation velocity,but both indicate that the topography between fronts does not change the eddy velocity.The results from the analysis of the hydrological characteristics within the eddies show that eddies with different polarities are able to achieve long-range transport of water masses from completely different sources,and for the same source water masses,the cyclonic eddies have a lifting effect,while the anticyclonic eddies have a depressing and sinking effect.This research work helps to improve the understanding of the characteristics and variability of the Southern Ocean eddies and supports further research on eddy dynamics.