Combining surface drifters and high resolution global simulations enables the mapping of internal tide surface energy

By dissipating energy and generating mixing, internal tides (ITs) are important for the climatological evolution of the ocean. Our understanding of this class of ocean variability is however hindered by the rarity of observations capable of capturing ITs with global coverage. The data provided by the Global Drifter Program (GDP) offer high temporal resolution and quasi-global coverage, thus bringing promising perspectives. However, due to their inherent drifting nature, these instruments provide a distorted view of the IT signal. By theoretically rationalizing this distortion and leveraging a massive synthetic drifter numerical simulation, we propose a global metric converting semi-diurnal IT energy levels from GDP data to levels comparable to Eulerian datasets (two numerical simulations, and a satellite altimetry IT atlas). We find that the simulation with a dedicated focus on IT representation is the one where the converted Lagrangian levels perform best. This supports renewed efforts in the concurrent numerical modeling of ITs/ocean circulation. The substantial deficit of energy in the IT atlas highlights the inability for altimetric estimates to measure incoherent and fine-scale ITs and strongly supports the need to isolate ITs signature in the data collected by the new wide-swath altimetry mission SWOT.