Internal Tide Energy Conversion
Internal tide energy conversion refers to the energy conversion from barotropic to baroclinic modes as surface tides flow over steep and rough topography in the deep ocean generating internal tides. The "lost" barotropic tidal energy is often accounted for through a linear friction term in large-scale numerical models that are barotropic or not fine-scaled enough to resolve the energy conversion. It is implemented in ADCIRC through a spatially varying nodal attribute called internal_tide_friction, in the fort.13 file.
Background and Theory
For a review.
In a computational domain covering a large portion of the deep ocean it is critical to include the effect of internal tide energy conversion to obtain more accurate tidal solutions. The user should only elect to use the internal_tide_friction nodal attribute when tides are included in the simulation through tidal boundary conditions and tidal potential functions. The attribute is unnecessary for domains that are small in size and/or do not cover a significant portion of the deep ocean (taken here to mean the portion of the ocean excluding the continental shelf).
ADCIRC reads the internal_tide_friction attribute in as the IT_Fric variable, which can have 1 (scalar) or 3 (tensor) dimensions. The attribute has dimensions of [1/time], meaning that it is a linear friction term which is multiplied by the velocity in the governing equations, and is normalized by the ocean depth prior to simulation. Hence, it ignores the water surface elevation portion of the total water depth, which is reasonable since the term and theory it is based on is only applicable to deep ocean. Typically, it is only applied to ocean depths greater than 100-500 m.
Specifying IT_Fric Values
IT_Fric values are determined through analytical formulations based on Bell's linear theory, valid in what is called sub-critical topography. Recent publications using ADCIRC provide relevant formulation and implementation details.
- C. Garrett, E. Kunze, Internal Tide Generation in the Deep Ocean, Annu. Rev. Fluid Mech. 39 (2007) 57–87. doi:10.1146/annurev.fluid.39.050905.110227.
- G.D. Egbert, R.D. Ray, Significant dissipation of tidal energy in the deep ocean inferred from satellite altimeter data, Nature. 405 (2000) 775–778. doi:10.1038/35015531
- G.D. Egbert, R.D. Ray, Estimates of M2 tidal energy dissipation from TOPEX/Poseidon altimeter data, J. Geophys. Res. Ocean. 106 (2001) 22475–22502. doi:10.1029/2000JC000699.
- T.H. Bell, Topographically generated internal waves in the open ocean, J. Geophys. Res. 80 (1975) 320–327. doi:10.1029/JC080i003p00320.
- W.J. Pringle, D. Wirasaet, A. Suhardjo, J. Meixner, J.J. Westerink, A.B. Kennedy, S. Nong, Finite-Element Barotropic Model for the Indian and Western Pacific Oceans: Tidal Model-Data Comparisons and Sensitivities, Ocean Model. 129 (2018) 13–38. doi:10.1016/j.ocemod.2018.07.003.
- W.J. Pringle, D. Wirasaet, J.J. Westerink, Modifications to Internal Tide Conversion Parameterizations and Implementation into Barotropic Ocean Models, EarthArXiv. (2018) 9. doi:10.31223/osf.io/84w53.