Presenter: Ritabrata Thakur (University of Michigan Ann Arbor)

Description:
We study a regional configuration of the Massachusetts Institute of Technology general circulation model (MITgcm), in the Northeast Pacific Ocean, forced by a global, internal-tide-resolving simulation at the lateral boundaries.  Our goal is to understand the vertical structure of the internal gravity wave continuum and its sensitivity to model resolution and mixing parameters. These ocean simulations are forced both with realistic atmospheric fields as well as with astronomical tidal potential. We study the impact on vertical-wavenumber spectra of kinetic energy due to changes in K-Profile Parameterization (KPP) parameters and in horizontal and vertical resolution, progressively increasing resolution from a base simulation that has 88 vertical levels and 2-km horizontal grid spacing. We find that switching off the KPP background diffusivity and viscosity improves the kinetic energy spectra even for medium resolution (2-km horizontal grid spacing and 109 vertical levels). This improved representation provides the first hint that (a) a slight increase in the resolution of regional models improves the internal-wave vertical wavenumber spectrum and (b) KPP parameters need to be adjusted in order to more accurately represent the internal wave spectrum in internal-wave-admitting simulations. We also study the vertical wavenumber spectra of shear and strain and attempt to develop mixing parameterizations based on these high-resolution ocean simulations. The improved representation of small-scale ocean dynamics in these simulations makes them suitable for the development and evaluation of satellite missions like SWOT.