Modulation of internal solitary waves by the Kuroshio in the northern South China Sea.

Internal solitary waves (ISWs) in the South China Sea (SCS) are considerably modulated by the background currents. In this study, a three-dimensional high-resolution non-hydrostatic model is configured to investigate how the Kuroshio influences the generation and evolution of ISWs in the northern SCS. Three runs are conducted, including one control experiment without the Kuroshio and two sensitivity experiments with the Kuroshio in different paths. In the Luzon Strait (LS), the Kuroshio reduces the westward baroclinic energy flux radiated into the SCS, resulting in weakened ISWs. In the SCS basin, the background currents further refract the ISWs. With the leaping Kuroshio, the A-waves have longer crest lines but lower amplitudes compared with those in the control run. In contrast, the B-waves are less affected by the leaping Kuroshio. In the presence of looping Kuroshio, the wave refraction caused by the intrusion currents in the SCS basin results in the weakest amplitudes and energy but the widest crest lines of ISWs. Moreover, the energy of the A-waves exhibits double-peak structure along the crest lines. The crest lines of the B-waves extend to 19.5° N, which are more south than those in summer. These results highlight the importance of the Kuroshio on the 3D features of ISWs in the SCS.

Diurnal and semidiurnal internal waves on the southern slope of the Yermak Plateau.

The Yermak Plateau (YP) is located across the Arctic-Atlantic gateway in the northwest of the Svalbard archipelago. In this region, internal waves are believed to cause intense turbulent mixing and hence influence the heat budget in the Arctic Ocean. Based on year-long observations from three moorings, the characteristics and energetics of diurnal and semidiurnal internal waves on the southern slope of the YP are investigated in this study. Diurnal internal waves induce large isothermal displacements exceeding 100 m, which are nearly one order of magnitude greater than those of semidiurnal internal waves. In addition, diurnal internal waves are strong in winter but weak in summer, while the semidiurnal internal waves exhibit complicated temporal variation. For the diurnal internal waves, their available potential energy is greater than the horizontal kinetic energy; whereas the situation is opposite for the semidiurnal ones. This feature is further clarified with two-dimensional numerical simulations. Due to the larger tidal excursion, diurnal tidal forcing yields the generation of stronger higher harmonics, i.e., the semidiurnal internal waves. In contrast, higher harmonics are rather weak under the semidiurnal forcing. Moreover, a large proportion of energy for both diurnal and semidiurnal internal waves is dissipated locally. Results of this study can provide useful insight on the dynamics of internal waves in the Arctic Ocean.