the 22nd Pacific−Asian Marginal Seas meeting (PAMS)

Near-inertial waves (NIWs) are wind-driven internal motions with frequencies near the local inertial frequency f. They move energy from the atmosphere into the ocean interior and can enhance vertical mixing. The Southeast Indian Ridge (SEIR), located south of the Pacific, is a key place where the Antarctic Circumpolar Current (ACC) is particularly strong, which can influence the advection and dispersion of NIWs. Since November 2021, an array of sixteen Current- and Pressure-recording Inverted Echo Sounder (CPIES) has been deployed in the SEIR, and all data were successfully obtained through 2025. In addition, a tall mooring equipped with multiple current meters was deployed from 2022 to 2024. Using multi-year observation across the SEIR, we analyzed the temporal and spatial distribution of NIW energy. Deep NIW energy was estimated by applying a band-pass filter to the current meter time series from CPIES, while multi-depth measurement of NIW energy was also calculated from tall mooring data and was compared with relative vorticity (ζ) derived from AVISO surface absolute geostrophic velocity. While the slab model calculated with ERA5 wind data showed little spatial variability, the observed deep NIWs kinetic energy exhibited distinct localized hotspots which spatially coincided with regions of positive ζ in the upper layer. This study suggests that deep NIW energy is not uniformly distributed but is strongly modulated by upper layer circulation, with positive vorticity regions serving as preferential sites for energy intensification. Also, this result provides observational evidence that upper-layer relative vorticity governs the spatial pattern of deep NIW energy and implies the importance of continuous observations in the Southern Pacific and Southern Ocean for better understanding of the processes linking surface circulation and deep ocean mixing.

near-inertial waves,CPIES,ACC,relative vorticity