Observations of the Low‐Mode Internal Tide and Its Interaction With Mesoscale Flow South of the Azores

Understanding the temporal variability of internal tides plays a crucial role in identifying sources and sinks of energy in the ocean. Using a 10‐month‐long time series from moored instruments inside a tidal beam south of the Azores, the magnitude and the underlying causes of temporal variability in the first two modes of the internal tide energy flux was studied. We analyzed changes of the direction and coherence of the energy flux, its modal structure, and the impact of two eddies. Semidiurnal energy fluxes were further compared with estimates from a 1/10° ocean global circulation model, as well as with fluxes derived from satellite altimetry. All energy fluxes correlate reasonably well in direction, deviations from its fixed phase relation to astronomical forcing, and modal composition while model and satellite underestimate the total energy flux. A pronounced damping of the in situ fluxes coincides with the passing of two eddies. In the presence of a surface‐intensified eddy, the coherent part of the energy flux in the first two modes is lowered by more than 40%, a subsurface eddy coincides with a decrease of the energy flux mainly in the second mode. These observations support the hypothesis that eddy interactions increase the incoherent part of the energy flux and transfer energy from low modes into higher modes, which can lead to increased local dissipation. It remains an open question how much of the energy converted from lower to higher modes results in local dissipation, a crucial part in creating energetically consistent ocean‐climate models. Plain Language Summary Internal tides are generated when a tidal wave interacts with underwater obstacles. These waves inside the water column transport energy throughout the ocean until they break and mix the water. Because this mixing is important for the ocean circulation and our climate, it is necessary that we understand all aspects of their behavior. In this study, we use year‐long observations of internal tides and their energy in a region south of the Azores Islands in the northeast Atlantic, where they are particularly strong. We compare our measurements with results from satellites and a global ocean circulation model and analyze the influence of eddies on internal tide energy. Eddies are common large‐scale vortices in the ocean which can make internal tides dissipate locally, hence making their energy available for local mixing. Our measurements show a decrease in energy flux by about one third w