Characteristics and Dynamics of the Interannual Eddy Kinetic Energy Variation in the Central Pacific Sector of the Southern Ocean

Abstract

Mesoscale eddies play a crucial role in the dynamical balance of the Southern Ocean (SO) circulation. Yet, it remains unclear why the SO transient eddy activity has significant variations on interannual time scales, and to what extent these low‐frequency variations are attributed to wind forcing changes. Here we use a functional analysis tool, namely, the multiscale window transform (MWT), the MWT‐based theory of canonical transfer and a time‐dependent energetics framework to investigate these issues. Our focus is on the central Pacific sector of the SO in which there is a significant time‐mean and interannual variability of the eddy kinetic energy (EKE). It is found that wind stress does not directly contribute to the interannual EKE variability through wind power injection to the eddies; instead, the influence is fulfilled indirectly through two internal pathways. First, the baroclinic pathway in which the wind‐generated mean kinetic energy (MKE) is converted to the mean available potential energy (APE), and is further released to eddy APE and finally to EKE through baroclinic instability, is the dominant one. Second, the barotropic pathway, in which MKE directly fuels EKE through barotropic instability, is faster but secondary, and its influence is only concentrated along the axis of the Antarctic Circumpolar Current. Our results highlight the dynamical connections between the internal and external processes in the SO energy system, and provide insights into the predictability of the SO eddies on interannual time scales.

Strong Eddy Kinetic Energy Anomalies Induced by Baroclinic Instability in the Southwest Region of the Kerguelen Plateau, East Antarctica

“…48670/moi-00021) acquired from Copernicus Marine Environment Monitoring Service (CMEMS) is employed to investigate the time-varying energetics, limited by the scarcity of in-situ observation in polar regions. The GLORYS12V1 is a global ocean eddy-resolving reanalysis product with a horizontal resolution of 1/12°× 1/12°a nd 50 vertical levels, spanning the altimetry era from 1993 onward, which has been used to analyze energetics in the Southern Ocean (G. Fu et al, 2023). Utilized three-dimensional monthly and daily variables including sea surface height (SSH), current velocity, potential temperature, and salinity across all vertical levels from 1993 to 2020.…”

“…The Lorenz energy cycle (Lorenz, 1955) is an effective approach to investigating the variability of a current system and quantitatively describing energy transfer among reservoirs, providing insights into the underlying ocean dynamics (e.g., Dong et al, 2022;Ivchenko et al, 1997;Kang & Curchitser, 2015;Rieck et al, 2015;von Storch et al, 2012). It has been extensively employed in analyzing energetics in the Southern Ocean (e.g., Chen et al, 2014Chen et al, , 2016G. Fu et al, 2023;Youngs et al, 2017).…”

“…The results demonstrated that the westerlies can locally supply sufficient energy to initiate baroclinic instability in the Indian and Pacific sectors of the ACC. In the central Pacific sector, the interannual variation of EKE in the upper ocean layer has revealed that wind stress impacts the variation through both baroclinic and barotropic pathways (G. Fu et al, 2023). Despite having a high level of eddy activity in the Indian sector, the energetics dynamics and EKE modulations in the confluence region between the ACC and subpolar gyre remain poorly explored, and the understanding of physical processes governing eddy energy in this subpolar region remains rather limited.…”

Strong Eddy Kinetic Energy Anomalies Induced by Baroclinic Instability in the Southwest Region of the Kerguelen Plateau,East Antarctic

“…The reanalysis data acquired from the Global Ocean Reanalysis and Simulation (GLORYS12V1) product were used to investigate the time-varying energetics in this study, limited by the scarcity of in-situ observation. This product is the Copernicus Marine Environment Monitoring Service (CMEMS) global ocean eddy-resolving (1/12° horizontal resolution, 50 vertical levels) reanalysis covering the altimetry (1993 onward), which has been used to analyze energetics in the Southern Ocean [Fu et al, 2023]. Utilized monthly and daily variables include sea surface height, current velocity, potential temperature, and practical salinity in all vertical levels, from 1993 to 2020.…”

“…The results demonstrated that the westerlies can locally supply sufficient energy to initiate baroclinic instability in the Indian and Pacific sectors of the ACC. In the central Pacific sector, the interannual variation of EKE in the upper ocean layer has revealed that wind stress impacts the variation through both baroclinic and barotropic pathways [Fu et al, 2023]. However, the Indian sector remains poorly explored.…”