Generation and Propagation of M₂ Internal Tides Modulated by the Kuroshio Northeast of Taiwan

Abstract

The variability and energetics of M2 internal tides during their generation and propagation through the Kuroshio flows northeast of Taiwan are investigated using a high‐resolution numerical model. The corrugated continental slopes, particularly the I‐Lan Ridge and Mien‐Hua Canyon, are first identified as the energetic sources of M2 internal tides. The domain‐integrated M2 barotropic‐to‐baroclinic conversion rate under the Kuroshio influence is ~2.35 GW, ~0.9 GW of which is generated at the I‐Lan Ridge, ~0.93 GW at the Mien‐Hua Canyon, and ~0.52 GW at the north shelf. The M2 internal tide generation is influenced by the horizontally varying, zonally tilting stratification associated with the Kuroshio. In this situation, the conversion rate decreases by ~30% at the I‐Lan Ridge but increases to within ~10% at the Mien‐Hua Canyon and north shelf, in comparison to the simulation initiated with horizontal homogeneous stratification. Internal tides from multiple sources interfere to form a three‐dimensional baroclinic field. The interference by the internal tides from the Mien‐Hua Canyon and north shelf is refracted by the Kuroshio and exhibits a mesoscale gyre pattern, which can explain the frequent occurrence of internal solitary waves. An energetic along‐slope tidal beam (TBKC) from the I‐Lan Ridge radiates southward against the northward Kuroshio flows, causing strong vertical displacement, which favorably compares with recently reported field measurements. The M2 internal tide energy dissipates primarily near the source sites, and the remaining energy radiates outward over limited distances. Complex topographic features and background currents enhance the internal tide dissipation, which induces strong, inhomogeneous diapycnal mixing.

Variation of Internal Tides on the Continental Slope of the Southeastern East China Sea

“…The dominant coherent semidiurnal ITs suggested that in November, the ITs remained phaselocked with the local barotropic tides, and they were generated in the vicinity of the observation site. The Mien-Hua Canyon and North Mien-Hua Canyon are the closest significant generation sites of semidiurnal ITs [23,25,27], and they are the probable generation sites of the observed semidiurnal ITs. Vertical modes of the semidiurnal internal tides in October and November are shown in Figure 7.…”

“…The East China Sea (ECS) have a wide continental shelf and a deep trough (the Okinawa Trough) connected by a steep continental slope. The generation of ITs in the ECS has been reported based on observations [19][20][21][22][23][24] and numerical models [25][26][27]. Lien et al found that on the continental slope to the northeast of Taiwan Island, the semidiurnal internal tidal energy flux exhibits strong temporal and spatial variations, and it has a seaward direction [23].…”

“…Lien et al found that on the continental slope to the northeast of Taiwan Island, the semidiurnal internal tidal energy flux exhibits strong temporal and spatial variations, and it has a seaward direction [23]. The Mien-Hua Canyon, the I-Lan Ridge, and the continental shelf are the main IT generation sites in the ECS to the northeast of Taiwan [27]. The Kuroshio current is a strong west boundary current that flows across the ECS, and the Mien-Hua Canyon is one of the key passages by which the Kuroshio intrudes into the ECS [28,29].…”

Enhanced internal tidal mixing in the Philippine Sea mesoscale environment

“…When the internal tide passes through a mesoscale eddy, the energy of the mode 1 internal tide can be refracted and transmitted to higher-mode waves (e.g., Farrari and Wunsch, 2008;Henning and Vallis, 2005). The eddy flows can also directly increase vertical shear and, subsequently, the internal tide energy dissipation rate (e.g., Chavanne et al, 2010;Dunphy and Lamb, 2014). The anticyclones induce higher tidal mix-ing than cyclones, probably because of the chimney effects associated with distinct vorticities (Jing et al, 2011).…”

The Three‐Dimensional Internal Tide Radiation and Dissipation in the Mariana Arc‐Trench System

“…Likewise, the CTRL magnitudes were similar to those of TPXO7.2 and both decreased from west to east in both Figures 3a and 3b. Small-scale variations of the cophase lines near the ridges in Figure 3a reflect the impact of the M 2 baroclinic tides (Chang et al, 2019;Niwa & Hibiya, 2004). To provide a quantitative assessment of the modeled barotropic tides, the absolute root-mean-square error (RMSE) was calculated following Cummins and Oey (1997),…”