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
The basic theory for generation of internal tides in the deep ocean was established several decades ago. However, it was not thought to be incredibly important to the global energy balance of the surface tides until the modern satellite era when it was discovered that internal tides are responsible for approximately 30% of the global barotropic tidal dissipation.
Following this revelation the past two decades have been subject to a number of theoretical     and numerical    investigations into internal tide generation and their effects on the surface tides through parameterizations.       
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
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