836 / 2024-09-19 16:04:25

Tidal Energetics in Eddying ocean: An investigation in the South China Sea

internal tides,energy budget,decay scale,mode

Session 70 - Internal Waves and Ocean Mixing

The generation, propagation and dissipation of internal tides determine the energy distribution and mixing in the global ocean, and are also significantly affected by the background currents and stratification. Circulations, eddies and the other oceanic phenomena in the South China Sea have multiple spatial and temporal scales. Therefore, it’s necessary to investigate the tidal energetics under the effects of time-varying background fields in the SCS. In this talk, we use the model output from the high-resolution (1/48°) LLC4320 simulation of MITgcm to reveal the tidal energetics and associated budgets in the SCS involving the impacts of the background field. Analysis of the barotropic tidal energy budget highlights significant work rate of K1 tide-generating force in the SCS, whereas analysis of the baroclinic tidal energy budget reveals impacts of background fields on the energy conversion from the barotropic to baroclinic tides and the dissipation of baroclinic tidal energy. The seasonal variability of tidal dynamics and energetics further highlights modulations by background fields. An exponential decay of the baroclinic tidal energy flux with the distance from the generation site is revealed, and the decay scales for the K₁ and M₂ baroclinic tides in the SCS is estimated. A simple scaling of the baroclinic tidal energy flux in the SCS, which may be used to characterize tidal mixing in large-scale ocean and climate models, is thus devised. Next, the Sturm-Liouville equation, solved by a spectral method, is employed to investigate different responses of internal tides in different modes, as well as to derive the energy flux decay scales of internal tides. The results indicate that though the seasonal differences are obvious among each mode, these differences cancel out when all modes are superimposed together. It is expected to have a fundamental contribution to the parameterizations of tidal mixing.