LAUSR

Internal-tide generation has been quantified using both pressure work and energy conversion. When calculating the pressure work from simulated or observed data, the internal-tide pressure has to be decomposed from the full pressure, for which various options exist. We show that the conversion, that has to be derived from the depth-integrated energy equations, contains the work done by both the form drag at the bottom and that at the surface, with the latter being about 1% of the former. For calculating the pressure work, the internal-tide pressure identified as the deviation from the depth-averaged pressure perturbation has to be used. We analyzed the work done by the bottom form drag in STORMTIDE2, a concurrent simulation of circulations and tides. As expected, the identified internal-tide pressure reveals the characteristic pressure drop from the windward to the leeward side of an obstacle. The M2 internal-tide generation in STORMTIDE2 is more strongly controlled by the barotropic tide than by the topographic slope, partly because the tidal velocity can change up to one order of magnitude from the top to the foot of a high ridge within a short distance, a feature only produced by a high-resolution model. Consequently, the intense generation maps the immediate proximities of the summits of high ridges, making the global generation to be strongest near 1,200 m and decreasing drastically below 3,000 m. The depth structure of the generation differs in different basins, which could impact differently on circulations in different basins. Plain Language Summary Breaking of internal tides provides an important energy source for the oceanic meridional overturning circulation. In this context, it is crucial to fully understand and to accurately estimate the internal-tide generation. So far there exist different expressions for quantifying the internal-tide generation. This paper sorts this out by examining these expressions using equations of motions and STORMTIDE2, a concurrent simulation of circulations and tides. Crucial for the expression is the internal-tide pressure which needs to be identified from the full pressure. We show that the identified internal-tide pressure performs in the way as expected from our understanding of the work done by a form drag. For the M2 internal tide in STORMTIDE2, the intense generation is located in the proximities of the summits of high obstacles, leading to the stronger generation at roughly 1,200 m than further below. This dependence on depth differs in different ocean basins and can impact the diapycnal mixing and the circulation differently in different basins.