We investigate the interactions between breaking internal waves (IWs) and ocean diapycnal diffusivity using a high-resolution regional ocean model focused on the North Pacific region near Hawaii. Utilizing dynamically downscaled data from the global LLC4320 simulation, which incorporates both tidal and atmospheric forcing, we systematically analyze IW-breaking process and quantify its contribution to oceanic mixing. Our results indicate that the regional IW field is predominantly characterized by low-order modes, consistent with eigenvalue solutions of stratified flow.

A modified K-Profile Parameterization (KPP) is employed to characterize the vertical structure of diapycnal diffusivity and evaluate its consistency with global climate model representations. Particularly, deactivating the background component of KPP leads to redistribution of energy from lower to higher IW vertical modes, thereby facilitating a wave-turbulence cascade through triad resonance interactions and invigorating higher order modes. This cascade intensifies vertical shear and turbulent mixing, yielding diapycnal diffusivity profiles that better match observational data and empirical models such as the Garrett-Munk spectrum.

Furthermore, we implement the Bouffard-Boegman (BB) parameterization, which effectively distinguishes between reversible and irreversible mixing components. This parameterization enhances the accuracy of inferred diapycnal diffusivity profiles derived from turbulent dissipation rates, addressing significant limitations of previous KPP-based methodologies.

Overall, our findings highlight inherent deficiencies in the KPP framework, notably its tendency to overestimate shear-driven mixing, and underscore the critical role of accurately parameterized IW-breaking processes in determining vertical mixing structures. These vertical mixing dynamics substantially influence large-scale ocean circulation patterns and have profound implications for climate sensitivity projections.