The Importance of Remote Forcing for Regional Modeling of Internal Waves

Assimilation of Surface Water and Ocean Topography (SWOT) data will require models capable of representing oceanic processes on the 10-km scales that the satellite will resolve. Simulating dynamics on these scales is computationally demanding, motivating the use of regional domains. These regional models are generally forced at the boundaries by mesoscale ocean dynamics and barotropic tides. In this work we provide evidence that remotely forced internal waves can be a significant source of energy for the regional dynamics. We compare global and regional model solutions within the California Current System. Both models have similar inputs, forcings, grids, and numerics. The global model has a steric height power spectrum consistent with mooring observations at super-inertial frequencies, while the regional model spectrum is weaker. The regional model also has less sea surface height variance at high wavenumber than the global model. The vertical velocity variance is significantly larger in the global model, except in the sheltered Southern California Bight. While the regional model has roughly equal high-pass baroclinic and barotropic kinetic energy levels, the global model high-pass baroclinic kinetic energy is 28% (0.39 PJ) greater than the barotropic energy. An internal wave energy flux analysis reveals that the regional model domain boundaries act as a 183 MW sink, while in the global model the analysis domain boundaries act as a 539 MW source. This 722 MW difference can account for the relative increase of 0.39 PJ high-pass baroclinic energy in the global model, assuming a baroclinic kinetic energy dissipation time in the domain of approximately 6.3 days. The results here imply that most regional ocean models will need to account for internal wave boundary fluxes in order to reproduce the observed internal wave continuum spectrum.