Improved Internal Wave Spectral Continuum in a Regional Ocean Model

Abstract

Recent work demonstrates that high‐resolution global models forced simultaneously by atmospheric fields and the astronomical tidal potential contain a partial internal (gravity) wave (IW) spectral continuum. Regional simulations of the MITgcm forced at the horizontal boundaries by a global run that carries a partial IW continuum spectrum are performed at the same grid spacing as the global run and at finer grid spacings in an attempt to fill out more of the IW spectral continuum. Decreasing only the horizontal grid spacing from 2 to 0.25 km greatly improves the frequency spectra and slightly improves the vertical wavenumber spectra of the horizontal velocity. Decreasing only the vertical grid spacing by a factor of 3 does not yield any significant improvements. Decreasing both horizontal and vertical grid spacings yields the greatest degree of improvement, filling the frequency spectrum out to 72 cpd. Our results suggest that improved IW spectra in regional models are possible if they are run at finer grid spacings and are forced at their lateral boundaries by remotely generated IWs. Additionally, consistency relations demonstrate that improvements in the spectra are indeed due to the existence of IWs at higher frequencies and vertical wavenumbers when remote IW forcing is included and model grid spacings decrease. By being able to simulate an IW spectral continuum to 0.25 km scales, these simulations demonstrate that one may be able to track the energy pathways of IWs from generation to dissipation and improve the understanding of processes such as IW‐driven mixing.Plain Language SummaryModels of internal waves (IWs) may help us to better understand the spatial geography of mixing in the ocean and are playing an increasingly important role in the planning of satellite missions. Following recent work showing that high‐resolution global models contain a partial IW spectrum, this paper describes further improvements in the spectrum seen in a high‐resolution regional model forced at the boundaries by a previously performed global IW simulation. Decreasing only the horizontal grid spacing greatly improves the frequency spectra and slightly improves the vertical wavenumber spectra of velocity. Increasing only the number of vertical levels does not yield any significant improvements. Decreasing both horizontal and vertical grid spacings yields the greatest improvement in both spectra. Our results suggest that regional models can exhibit improved IW spectra over global models if two conditions are met—they must have higher horizontal and vertical resolutions, and they must have remotely generated IWs at their boundaries. Application of the so‐called consistency relations demonstrates that the model is indeed carrying a field of high‐frequency IWs. Being able to simulate a fuller IW spectrum demonstrates that one may be able to use these models to improve the understanding of IW‐driven processes and energy pathways.Key PointsInternal gravity wave spectra in regional models are more realistic as model grid spacing decreasesThe vertical wavenumber spectra improve less dramatically than the frequency spectraInternal gravity wave consistency relations are applied to modeled spectra