10:15 〜 10:30
[ACG47-06] Topographic Rossby waves on the ocean-side slope of the Kuril trench
キーワード：地形性ロスビー波、海溝、表層渦、係留観測
Topographic Rossby waves are commonly observed over continental shelves worldwide. However, their presence on the slope of a trench, particularly on its ocean-facing side, has rarely been documented. Trench slopes, especially in the northwestern Pacific, have a characteristic north-south orientation, but their detailed wave dynamics remain largely unknown.
To investigate deep current variability, a two-year mooring observation was conducted from August 2020 to April 2022. Each mooring station was equipped with three current meters at depths of approximately 3500 m, 4500 m, and 5500 m, recording velocity time series.
The analysis results revealed transient, bottom-trapped topographic Rossby waves with a 50-day period on the ocean-facing side of the trench slope. Topographic Rossby waves were identified through frequency analysis, based on their columnar structure, linear fluctuation, and frequency-dependent wave vector rotation, which was consistent with the theoretical dispersion relation. Complex empirical orthogonal function (CEOF) analysis of velocity data from two mooring stations demonstrated that their phase propagated upslope, with a local wavelength of approximately 40 km. Ray tracing calculations, based on the observed wave parameters, indicated that its energy propagated downslope.
The likely energy source was surface perturbations induced by an anticyclonic eddy, detected from AVISO data, which stagnated over the trench during the period of the dominant topographic Rossby wave activity. The location of the surface perturbations was consistent with the back-traced ray path of the waves. The inferred energy pathway from the surface eddy field to the deep ocean through wave generation and the downslope energy propagation suggests a robust mechanism for transferring energy from mesoscale eddies to deep ocean.
These findings highlight the role of topographic Rossby waves in modulating deep circulation along the trench slopes, providing new insights into deep ocean dynamics in regions where such processes have been previously undocumented.
To investigate deep current variability, a two-year mooring observation was conducted from August 2020 to April 2022. Each mooring station was equipped with three current meters at depths of approximately 3500 m, 4500 m, and 5500 m, recording velocity time series.
The analysis results revealed transient, bottom-trapped topographic Rossby waves with a 50-day period on the ocean-facing side of the trench slope. Topographic Rossby waves were identified through frequency analysis, based on their columnar structure, linear fluctuation, and frequency-dependent wave vector rotation, which was consistent with the theoretical dispersion relation. Complex empirical orthogonal function (CEOF) analysis of velocity data from two mooring stations demonstrated that their phase propagated upslope, with a local wavelength of approximately 40 km. Ray tracing calculations, based on the observed wave parameters, indicated that its energy propagated downslope.
The likely energy source was surface perturbations induced by an anticyclonic eddy, detected from AVISO data, which stagnated over the trench during the period of the dominant topographic Rossby wave activity. The location of the surface perturbations was consistent with the back-traced ray path of the waves. The inferred energy pathway from the surface eddy field to the deep ocean through wave generation and the downslope energy propagation suggests a robust mechanism for transferring energy from mesoscale eddies to deep ocean.
These findings highlight the role of topographic Rossby waves in modulating deep circulation along the trench slopes, providing new insights into deep ocean dynamics in regions where such processes have been previously undocumented.