An observational study of coastal trapped wave scattering in the deep ocean of the Suruga Trough: the role of internal lee waves

Abstract In this study, the scattering and dissipation processes of diurnal coastal trapped waves (CTWs) are investigated using mooring observations and direct microstructure measurements in the Suruga Trough, Japan. First, we perform spectral and harmonic analyses of the observed data, confirming the presence of diurnal CTWs characterized by velocity and temperature perturbations that are most pronounced near the seafloor. The interaction of bottom-intensified CTW currents with a small-scale bathymetric bump generates high-frequency waves, exhibiting spectral peaks at the harmonics of the diurnal tidal constituents. These high-frequency waves are identified as internal lee waves based on the dispersion relationship and are responsible for strong mixing on the lee side of the bathymetric bump, as evidenced by microstructure measurements. Using moored velocity records, we further examine the parameter dependence of internal lee wave generation by CTWs propagating over the bathymetric bump. The results indicate that internal lee wave activity intensifies when the tidal excursion parameter $${T}_{e}$$ falls within an intermediate range between 1 and the stratification parameter $${N}^{*}$$ . In contrast, when $${T}_{e}$$ exceeds $${N}^{*}$$ , the energy of internal lee waves decreases markedly due to the formation of “evanescent waves” resulting from strong interactions between CTWs and the bathymetric bump.