Gravity waves are waves for which gravity acts as the restoring force. Internal gravity waves are waves that exist because of stratification—e.g., the differences in density between lighter waters in the upper ocean and heavier waters in the deep ocean. When parcels oscillate up-and-down in a stratified fluid, there is a gravitational restoring force due to the differences in density between fluids at different vertical levels. Internal tides are internal gravity waves with tidal frequencies. The internal gravity wave continuum consists of gravity waves with supertidal frequencies e.g., frequencies that are greater than the tidal frequency.
Our group has been involved in several key steps on the path towards global modeling of internal tides and the internal gravity wave continuum.
Because of the atmospheric forcing, the internal tides in such simulations propagate in a realistic horizontally varying stratification, thus allowing for realistic comparisons of modeled vs. observed internal tides (Timko et al. 2012, 2013).
Mesoscale eddies scatter low-mode internal tides, thus rendering some of the internal tide energy incoherent. We have quantified this effect in different ways in Shriver et al. (2014), Ansong et al. (2017), Savage et al. (2017), and Buijsman et al. (2017).
Savage et al. (2017) made global maps of the non-steric and steric sea surface height (SSH) variance in different frequency bands. The map below shows the steric SSH variance in non-stationary semidiurnal tides and supertidal internal gravity wave continuum motions, both of which will be difficult to extract from satellite altimeter data, which suffers from temporal aliasing problems.
Timko et al. (2018—in review) showed that global models with simultaneous atmospheric and tidal forcing can sustain tidal mixing fronts on shelves. Timko et al. (2017) showed that models that employ an enhanced abyssal hill roughness as a stand-in for small-scale variations missing in global bathymetric products see an enhanced tidal energy conversion—see Melet et al. 2013 for a related study based upon linear wave theory. Buijsman et al. (2016) and Ansong et al. (2015) examine the impact of parameterized internal wave drag on the internal tides and tidal energy budgets in our multi-layer HYCOM tidal simulations. Ansong et al. (2015) built upon Shriver et al. (2012) who performed extensive comparisons of the internal tides in our HYCOM wind+tides simulations with along-track altimetry. Richman et al. (2012) demonstrated that the contributions of high-frequency motions to the sea surface height wavenumber spectrum—a quantity of fundamental interest in satellite altimetry—can be as large as the contributions from low-frequency motions.
On stratification, large-scale tides, and temporal changes in surface tidal elevations: Two-layer analytical model.
CURRENTLY IN REVIEW
On the interplay between horizontal resolution and wave drag and their effect on tidal baroclinic mode waves in realistic global ocean simulations
Statistical comparisons of temperature variance and kinetic energy in global ocean models and observations: Results from mesoscale to internal wave frequencies
Geographical distribution of diurnal and semidiurnal parametric subharmonic instability in a global ocean circulation model.
Frequency content of sea surface height variability from internal gravity waves to mesoscale eddies.
Semidiurnal internal tide energy fluxes and their variability in a global ocean model and moored observations.
Impact of synthetic abyssal hill roughness on resolved motions in numerical global ocean tide models.
Impact of parameterized internal wave drag on the semidiurnal energy balance in a global ocean circulation model.
On improving the accuracy of the M2 barotropic tides embedded in a high-resolution global ocean circulation model.
Inferring dynamics from the wavenumber spectra of an eddying global ocean model with embedded tides.
An evaluation of the barotropic and internal tides in a high resolution global ocean circulation model.
Skill tests of three-dimensional tidal currents in a global ocean model: A look at the North Atlantic.