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

Abstract

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.

Tides, Internal and Near‐Inertial Waves in the Yermak Pass at the Entrance of the Atlantic Water to the Arctic Ocean

“…“Baroclinic” velocities and shear spectra (Figures 9, 13, and 14; Figures S1 and S2 in Supporting Information ) show a dominant peak around the semi‐diurnal period while velocity spectra show a dominant peak at the diurnal frequency (Figure 3). This is consistent with recent mooring observations on the southwestern slope of the Yermak Plateau (6E, 79°40’) (Wang et al., 2022). Their observations suggest that a strong diurnal barotropic tide impinging on the slope can generate internal waves at higher harmonics, in particular, semi‐diurnal internal waves.…”

“…Possibly, interactions of freely propagating internal waves at period 2K1 (11.97 hr) generated and propagated from both eastern and western slopes of the rather narrow plateau could lead to stationary waves as observed here. Further moorings in the Yermak Plateau complementing observations by Wang et al (2022) on the southwestern slope and the present ones on the eastern slope are needed to test this hypothesis.…”

“…It was shown that the strength of the diurnal barotropic tide and the steepness of the slope are controlling factors in producing internal waves at higher harmonics and solitary waves. New mooring observations on the Southwestern slope of the Yermak Plateau documented strong barotropic diurnal tides triggering internal waves at higher harmonics, in particular at the semi‐diurnal period (Wang et al., 2022). It is to be noted that the second harmonic (period 11.97 hr) of the diurnal tide is not subinertial over the Yermak Plateau and could freely propagate.…”

Tides, Internal and Near-Inertial Waves in the Yermak Pass at the Entrance of the Atlantic Water to the Arctic Ocean.

“…"Baroclinic" velocities and shear spectra (Figures 9,13,and 14;Figures S1 and S2 in Supporting Information S1) show a dominant peak around the semi-diurnal period while velocity spectra show a dominant peak at the diurnal frequency (Figure 3). This is consistent with recent mooring observations on the southwestern slope of the Yermak Plateau (6E, 79°40') (Wang et al, 2022). Their observations suggest that a strong diurnal barotropic tide impinging on the slope can generate internal waves at higher harmonics, in particular, semi-diurnal internal waves.…”

“…It was shown that the strength of the diurnal barotropic tide and the steepness of the slope are controlling factors in producing internal waves at higher harmonics and solitary waves. New mooring observations on the Southwestern slope of the Yermak Plateau documented strong barotropic diurnal tides triggering internal waves at higher harmonics, in particular at the semi-diurnal period (Wang et al, 2022). It is to be noted that the second harmonic (period 11.97 hr) of the diurnal tide is not subinertial over the Yermak Plateau and could freely propagate.…”