Interannual Variation Characteristics And Dynamic Mechanism Of Eddy Kinetic Energy In The Pacific Sector Of The Southern Ocea

Mesoscale eddies play a crucial role in the dynamical balance of the Southern Ocean circulation.In this study,we use a new functional analysis tool,the multiscale window transform(MWT),to decompose the original oceanic fields into components on two orthogonal subspaces,i.e.,the background mean flow window and mesoscale eddy window.Within the MWT framework,we further employ the theory of canonical transfer in the light of energy conservation among scales and a time-dependent multiscale energetics framework to investigate the energetics of eddy-mean flow interactions and interannual modulation of the eddy kinetic energy(EKE),with a focus on the central Pacific sector of the Southern Ocean(CPSSO).It is found that the Antarctic Circumpolar Current in the CPSSO sector undergoes strong mixed instabilities.Baroclinic instability facilitates the eddy generation by transferring available potential energy(APE)from the background flow and further converting to the EKE,whereas barotropic instability feeds the eddy field by directly transferring the kinetic energy of the background flow to the EKE.These two instability energy pathways exhibit different spatial patterns,with the baroclinic one being the dominant EKE source in the whole region,while the barotropic source only confined along the jet axis in the upstream region.A budget analysis reveals that the EKE sources are balanced by energy dispersion through pressure work,and sub-grid dissipation.The EKE in the CPSSO sector has significant variations on interannual time scales.Using the time-dependent energetics analysis,we found that wind stress contributes to the interannual variability of the EKE in three different ways.The baroclinic pathway,in which the mean kinetic energy(MKE)is generated by the wind,converted to the mean available potential energy,and is further released to EKE through baroclinic instability,is the dominant one.The time lag of the response of EKE to the wind power injection is about 2.4 years.In contrast,the barotropic pathway,in which the MKE directly fuels the EKE through barotropic instability,is much faster but secondary,and its influence is only concentrated along the mean jet west of 140°W.The wind stress is also found to directly energize the eddy field,resulting in an almost simultaneous EKE response on interannual time scales.However,this direct pathway is much smaller in magnitude compared to the baroclinic and barotropic pathways.