Jeon, C. - H., Buijsman, M. C., Wallcraft, A. J., Shriver, J. F., Arbic, B. K., Richman, J. G., et al. (2019). Improving surface tidal accuracy through two-way nesting in a global ocean model. Ocean Modelling, 137, 98–113.
Abstract: In global ocean simulations, forward (non-data-assimilative) tide models generally feature large sea-surface-height errors near Hudson Strait in the North Atlantic Ocean with respect to altimetry-constrained tidal solutions. These errors may be associated with tidal resonances that are not well resolved by the complex coastal-shelf bathymetry in low-resolution simulations. An online two-way nesting framework has been implemented to improve global surface tides in the HYbrid Coordinate Ocean Model (HYCOM). In this framework, a high-resolution child domain, covering Hudson Strait, is coupled with a relatively low-resolution parent domain for computational efficiency. Data such as barotropic pressure and velocity are exchanged between the child and parent domains with the external coupler OASIS3-MCT. The developed nesting framework is validated with semi-idealized basin-scale model simulations. The M2 sea-surface heights show very good accuracy in the one-way and two-way nesting simulations in Hudson Strait, where large tidal elevations are observed. In addition, the mass and tidal energy flux are not adversely impacted at the nesting boundaries in the semi-idealized simulations. In a next step, the nesting framework is applied to a realistic global tide simulation. In this simulation, the resolution of the child domain (1/75°) is three times as fine as that of the parent domain (1/25°). The M2 sea-surface-height root-mean-square errors with tide gauge data and the altimetry-constrained global FES2014 and TPXO9-atlas tidal solutions are evaluated for the nesting and no-nesting solutions. The better resolved coastal bathymetry and the finer grid in the child domain improve the local tides in Hudson Strait and Bay, and the back-effect of the coastal tides induces an improvement of the barotropic tides in the open ocean of the Atlantic.
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Jeon, C. - H., Buijsman, M. C., Wallcraft, A. J., Shriver, J. F., Arbic, B. K., Richman, J. G., et al. (2019). Improving surface tidal accuracy through two-way nesting in a global ocean model. Ocean Modelling, 137, 98–113.
Abstract: In global ocean simulations, forward (non-data-assimilative) tide models generally feature large sea-surface-height errors near Hudson Strait in the North Atlantic Ocean with respect to altimetry-constrained tidal solutions. These errors may be associated with tidal resonances that are not well resolved by the complex coastal-shelf bathymetry in low-resolution simulations. An online two-way nesting framework has been implemented to improve global surface tides in the HYbrid Coordinate Ocean Model (HYCOM). In this framework, a high-resolution child domain, covering Hudson Strait, is coupled with a relatively low-resolution parent domain for computational efficiency. Data such as barotropic pressure and velocity are exchanged between the child and parent domains with the external coupler OASIS3-MCT. The developed nesting framework is validated with semi-idealized basin-scale model simulations. The M2 sea-surface heights show very good accuracy in the one-way and two-way nesting simulations in Hudson Strait, where large tidal elevations are observed. In addition, the mass and tidal energy flux are not adversely impacted at the nesting boundaries in the semi-idealized simulations. In a next step, the nesting framework is applied to a realistic global tide simulation. In this simulation, the resolution of the child domain (1/75°) is three times as fine as that of the parent domain (1/25°). The M2 sea-surface-height root-mean-square errors with tide gauge data and the altimetry-constrained global FES2014 and TPXO9-atlas tidal solutions are evaluated for the nesting and no-nesting solutions. The better resolved coastal bathymetry and the finer grid in the child domain improve the local tides in Hudson Strait and Bay, and the back-effect of the coastal tides induces an improvement of the barotropic tides in the open ocean of the Atlantic.
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Timko, P. G., Arbic, B. K., Hyder, P., Richman, J. G., Zamudio, L., O'Dea, E., et al. (2019). Assessment of shelf sea tides and tidal mixing fronts in a global ocean model. Ocean Modelling, 136, 66–84.
Abstract: Tidal mixing fronts, which represent boundaries between stratified and tidally mixed waters, are locations of enhanced biological activity. They occur in summer shelf seas when, in the presence of strong tidal currents, mixing due to bottom friction balances buoyancy production due to seasonal heat flux. In this paper we examine the occurrence and fidelity of tidal mixing fronts in shelf seas generated within a global 3-dimensional simulation of the HYbrid Coordinate Ocean Model (HYCOM) that is simultaneously forced by atmospheric fields and the astronomical tidal potential. We perform a first order assessment of shelf sea tides in global HYCOM through comparison of sea surface temperature, sea surface tidal elevations, and tidal currents with observations. HYCOM was tuned to minimize errors in M2 sea surface heights in deep water. Over the global coastal and shelf seas (depths <200 m) the area-weighted root mean square error of the M2 sea surface amplitude in HYCOM represents 35% of the 50 cm root mean squared M2 sea surface amplitude when compared to satellite constrained models TPXO8 and FES2014. HYCOM and the altimeter constrained tidal models TPXO8 and FES2014 exhibit similar skill in reproducing barotropic tidal currents estimated from in-situ current meter observations. Through comparison of a global HYCOM simulation with tidal forcing to a global HYCOM simulation with no tides, and also to previous regional studies of tidal mixing fronts in shelf seas, we demonstrate that HYCOM with embedded tides exhibits quite high skill in reproducing known tidal mixing fronts in shelf seas. Our results indicate that the amount of variability in the location of the tidal mixing fronts in HYCOM, estimated using the Simpson-Hunter parameter, is consistent with previous studies when the differences in the net downward heat flux, on a global scale, are taken into account. We also provide evidence of tidal mixing fronts on the North West Australian Shelf for which we have been unable to find references in the existing scientific literature.
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Morey, S. L., Wienders, N., Dukhovskoy, D. S., & Bourassa, M. A. (2018). Impact of Stokes Drift on Measurements of Surface Currents from Drifters and HF Radar. In American Geophysical Union (Vol. Fall Meeting).
Abstract: Concurrent measurements by surface drifters of different configurations and HF radar reveal substantial differences in estimates of the near-surface seawater velocity. On average, speeds of small ultra-thin (5 cm) drifters are significantly greater than co-located drifters with a traditional shallow drogue design, while velocity measurements from the drogued drifters closely match HF radar velocity estimates. Analysis of directional wave spectra measurements from a nearby buoy reveals that Stokes drift accounts for much of the difference between the velocity measurements from the drogued drifters and the ultra-thin drifters, except during times of wave breaking. Under wave breaking conditions, the difference between the ultra-thin drifter velocity and the drogued drifter velocity is much less than the computed Stokes drift. The results suggest that surface currents measured by more common approaches or simulated in models may underrepresent the velocity at the very surface of the ocean that is important for determining momentum and enthalpy fluxes between the ocean and atmosphere and for estimating transport of material at the ocean surface. However, simply adding an estimate of Stokes drift may also not be an appropriate method for estimating the true surface velocity from models or measurements from drogued drifters or HF radar under all sea conditions.
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Arbic, B. K., Wallcraft, A. J., & Metzger, E. J. (2010). Concurrent simulation of the eddying general circulation and tides in a global ocean model. Ocean Modelling, 32(3-4), 175–187.
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