Ocean General Circulation Models (OCGM) have been used for ocean forecasts and reanalysis in the past; successfully reproducing realistic large scale features such as Western Boundary Currents (WBC) which evolve slowly in time. Recent developments of three dimensional OCGM’s include the incorporation of tidal forcing embedded in the numerical integration. With the inclusion of higher frequency tidal forcing it is now possible to study the impact of tides on the larger scale features of the ocean reproduced in the OCGM’s such as WBC’s through comparison of simulations with and without tides. We compare two 1/12.5° simulations of the Hybrid Coordinate Ocean Model (HYCOM) and report on differences in the mean position, transports, and warm/cold core eddy production in the Gulf Stream and Kuroshio Current and their extensions across the Atlantic and Pacific Oceans.

The wavenumber spectral slope of sea surface height (SSH) computed within the mesoscale range from satellite altimetry exhibits a large spatial variability which, until now, has not been reproduced in numerical ocean models. This study documents the impacts of including internal tides, high-resolution bathymetry, and high-frequency atmospheric variability on the SSH wavenumber spectra in the Atlantic Ocean, using a series of 1/50° Equatorial and North Atlantic simulations with a realistic representation of barotropic/baroclinic tides and mesoscale-to-submesoscale variability. The results show that the inclusion of internal tides does increase high frequency SSH variability (with clear peaks near 120 km and 70 km) and flattens the spectra slope in the mesoscale range in a good agreement with observations. The surface signature of internal tides, mostly in the equatorial Atlantic but also in subtropical regions in the eastern North Atlantic, is the primary reason behind the observed large spatial variability of the spectral slope in the Atlantic. Internal tides are stronger in the tropical regions when compared to higher latitudes because of the stronger barotropic tides and stronger stratification in the upper layer of the water column. High-resolution bathymetry does play an important role in the internal tide generation on a local scale, but its impact on large-scale SSH variability and SSH wavenumber spectra is quite small. High-frequency wind variability plays only a minor role on the generation of high-frequency SSH variability.

On this poster we explore how well global HYbrid Coordinate Ocean Model (HYCOM) simulations predict (semidiurnal) internal tides and their decay. We explore two important factors that govern the internal tide predictability: model resolution (8 km vs. 4 km) and wave drag. We validate these simulations with internal-tide sea-surface height amplitudes from altimetry, surface-tide dissipation rates estimated from an altimetry-constrained model, finestructure and microstructure dissipation rates, and modal-conversion rates computed from analytical models. To compare HYCOM to various altimetry data sets, we derive a spatially varying correction factor that accounts for the effect of time series duration on non-stationarity. We perform tidal energy balances and decompose the M2 internal tides into vertical modes.