Representing the propagation and far-field dissipation of internal tides in a global climate model

Roughly half the mechanical energy input to abyssal mixing in support of global overturning circulation cascades from the barotropic tide through the internal tides down to turbulent scales. The low mode components of the internal tide redistribute much of this energy as they propagate thousands of kilometers from their generation sites prior to breaking into turbulence. Despite obvious climatic implications, the propagation and far-field dissipation of internal tides is largely unaccounted for in global climate models in which coarse grid resolution precludes their explicit representation. The current study works to resolve this issue through developing a new model of the propagating internal tides that is based on classic ray tracing techniques. Assuming weak interaction between modes, energy density corresponding to discrete modes and frequencies is horizontally advected using the local mode velocity and re-partitioned in angle orientation (refracted) according to the hydrostatic dispersion relation. The ray-tracing scheme is implemented in Geophysical Fluid Dynamic Laboratory’s MOM6 global ocean model using various parameterizations for the generation and dissipation of the internal tide, giving a complete prognostic prediction of both magnitude and spatial distribution of the far-field component of mixing due to the internal tides. The impact of far-field dissipation on the ocean state is assessed through fully-coupled climate simulations using GFDL’s ESM2G Earth System Model.