Observation of Topographic Rossby Waves Triggered by Kuroshio Path Meander in the East China Sea

초록

Topographic Rossby waves (TRWs) are motions triggered by potential vorticity adjustments, which strongly contribute to deep ocean variabilities. This study discerned near-36-day significant along-slope fluctuations, speculated to be TRWs, using deep current observations over the continental slope in the East China Sea (ECS). The TRWs propagated southwestward along the continental slope with wavelengths of similar to 95 km in the northern stations and similar to 36 km in the southern stations where the slope is steeper. The group velocity was estimated to be similar to 15.5 km/day, and the maximum current speed was similar to 10 cm/s. It was assumed that the energy source originates from the Kuroshio path meander, which has a similar typical period to the TRWs and can induce surface eddy kinetic energy, along with depth variations of water column in west of the Tokara Strait. Analyses involving ray tracing model of TRWs showed consistency with the observations in wave characteristics, thereby confirming our postulation regarding the TRWs and their origin. Moreover, the energy rays, emanated from the origin, intensively propagated along the slope; and after climbing over the successive slope, eventually stopped when reaching the flat areas. Additionally, the TRWs' hyperbolic intensification and vertical coherent phase features were revealed in model results. The seasonality of the Kuroshio path meander induced depth variation of water column was estimated to be prevalent in February and August. Overall, this study revealed the propagation features and generation mechanism of TRWs over the continental slope in the ECS for the first time.

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