Evaluating the Global Internal Wave Model IDEMIX with observations of both stratification and horizontal velocity

The model ‘Internal Wave Dissipation, Energy and Mixing’ (IDEMIX) provides an energetically consistent representation for the diapycnal diffusivity induced by breaking of internal gravity waves in ocean and atmosphere circulation models. IDEMIX predicts the internal wave energy, dissipation rates, and diapycnal diffusivities. Such small-scale processes cannot be resolved but have to be parameterized due to their relevance for the large-scale circulation. The basic version of the model has been shown to be generally successful in ocean and atmosphere applications. However, in regions of strong forcing deviations from observational estimates were found. To evaluate the local performance of the model we analyzed the agreement with observational estimates of full-depth profiles of both stratification and horizontal velocity collected by several cruises around 47°N and 16°N in the Atlantic. The hydrographic profiles come from two dynamically different regions: the subpolar North Atlantic with energetic wind-induced near-inertial waves and the western subtropical Atlantic where the strong Deep Western Boundary Current interacts with the continental slope producing lee waves. Internal wave energy, dissipation rates and diapycnal diffusivities estimates are obtained using the finestructure method. These estimates can be calculated using shear and strain or strain only in lack of velocity data. In this study, both formulations have been calculated and contrasted between each other to evaluate the importance of shear information for a realistic energy budget. The results when comparing IDEMIX with observations show that the higher differences are close to the surface and over the rough topography where internal gravity waves are more predominant. The analysis of the observational data will increase our understanding of the spatiotemporal variability of the ocean’s internal gravity wavefield and will complement the model-based investigation of the responsible processes.