Successful insertion of barotropic and baroclinic tides into a global 1/12 degree ocean general circulation model

In recent years, increasing computer power has allowed internal tide models to be run at high-resolution on a global scale (Arbic et al. 2004; Simmons et al. 2004; Hibiya et al. 2006; Simmons 2008). All of these models have been run as pure tide models (i.e., without wind and buoyancy forcing) with a horizontally uniform stratification (since the wind and buoyancy forcing required to support a nonuniform stratification is absent). We have recently completed a 5-year simulation in which the eight largest tidal constituents have been embedded into the HYCOM general circulation model, run globally at 1/12 degree resolution and with 32 vertical layers. The run includes realistic wind and buoyancy forcing. Hence a horizontally varying stratification as well as an energetic mesoscale eddy field are present in the model, and will interact with the internal tide field. We report here on some preliminary analyses of this simulation. The globally averaged rms elevation errors of the eight largest tidal constituents are comparable to those in previous forward tide models which include a tuned topographic internal wave drag. The amplitude and wavelength of the surface signature of internal tides compares well with that inferred from satellite altimetry data. The horizontally varying stratification leads to a very different surface signature of internal tides in polar regions, compared to results using a spatially uniform stratification. Ongoing and planned analyses of various aspects of the simulation--for instance eddy/tide interaction, the stationarity of internal tide beams, and the impact of tides on the general circulation, water masses, and the energy budget--will be briefly described. References Arbic, B.K., S.T. Garner, R.W. Hallberg, and H.L. Simmons, 2004: The accuracy of surface elevations in forward global barotropic and baroclinic tide models. Deep-Sea Research II 51, 3069-3101. Hibiya, T., M. Nagasawa, and Y. Niwa, 2006: Global mapping of diapycnal diffusivity in the deep ocean based on the results of expendable current profiler (XCP) surveys. Geophysical Research Letters 33, L03611, doi:10.1029/2005GL025218. Simmons, H.L., 2008: Spectral modification and geographic redistribution of the semi-diurnal internal tide. Ocean Modelling 21, 126-138. doi:10.1016/j.ocemod.2008.01.002 Simmons, H.L., R.W. Hallberg, and B.K. Arbic, 2004: Internal wave generation in a global baroclinic tide model. Deep-Sea Research II 51, 3043-3068.