Energy Sinks for Lee Waves in the Northern South China Sea

Abstract

Recent observations report a discrepancy between observed energy dissipation rates and lee wave pressure flux predicted by linear theory in the Southern Ocean, raising the possibility that wave energy re‐absorption by mean flows may be an important route to wave energy sink. Here we investigate the sink of lee waves in the northern South China Sea in a high‐resolution nested model initialized with a synthetically‐generated rough topography. Our results indicate that wave dissipation is the dominant sink of lee wave energy, with wave energy re‐absorption being of secondary importance. The dominant direction of energy transfer is from mean flows to lee waves through vertical shear and horizontal strain of mean flows. A series of idealized experiments suggest that the weak wave energy re‐absorption in the northern South China Sea is primarily due to the large Froude number there.

The Role of Small‐Scale Topography in Modulating Eddy Scale in the Northern South China Sea

“…(2017) also found similar results in a global model with parameterized wave drag and they hypothesized a short‐circuiting of barotropization in the presence of the wave drag. A possible explanation is that the enhanced viscous dissipation owing to the small‐scale topography is largely compensated by the reduction in bottom friction in ROUGH (We find the dominant sink of lee wave energy in our model is wave dissipation (Yang et al., 2023), although recent studies (e.g., Kunze & Lien, 2019; Wu et al., 2022) suggest the lee wave energy absorption by bottom‐intensified flows may be also important for the lee wave energy sink) (Yang et al., 2022). For example, the volume‐integrated (below 300‐m depth) viscous dissipation is found to be enhanced by 73% in ROUGH compared to SMOOTH (31.45 vs. 54.47 W) whereas the volume‐integrated bottom friction is reduced by 33% (39.2 vs. 26.36 W).…”

Greenhouse Warming Reduces Global Energy Conversion Into Oceanic Lee Waves

“…In addition to Fr, the lee wave energy flux is also regulated by the vertical structure of the bottom flow. Recent studies (e.g., Baker & Mashayek, 2021;Kunze & Lien, 2019;Sun et al, 2022;Wu et al, 2022;Z. Yang et al, 2023a) suggest that lee wave-geostrophic flow interactions can either transfer energy from lee waves to geostrophic flows or the opposite.…”

“…In addition to Fr , the lee wave energy flux is also regulated by the vertical structure of the bottom flow. Recent studies (e.g., Baker & Mashayek, 2021; Kunze & Lien, 2019; Sun et al., 2022; Wu et al., 2022; Z. Yang et al., 2023a) suggest that lee wave‐geostrophic flow interactions can either transfer energy from lee waves to geostrophic flows or the opposite. The greenhouse warming does not only affect N b and U b but also the vertical structure of geostrophic flows in the ocean interior (Peng et al., 2022), with the later playing a key role in the energy exchange between geostrophic flows and lee waves (Kunze & Lien, 2019).…”