Energy Flux Observations in an Internal Tide Beam in the Eastern North Atlantic

• Published in: Journal of geophysical research. Oceans 2019-08, Vol.124 (8), p.5747-5764
• Main Authors: Köhler, Janna, Walter, Maren, Mertens, Christian, Stiehler, Jan, Li, Zhuhua, Zhao, Zhongxiang, Storch, Jin‐Song, Rhein, Monika
• Format: Article
• Language: English
• Subjects: Altimeters; Basins; Climate; Climate models; Computer simulation; Energy; Energy dissipation; Energy exchange; Energy flux; Energy losses; Energy transfer; Finestructure; Fluctuations; Fluxes; General circulation models; Geophysics; In situ measurement; Internal tidal waves; internal tide; Internal tides; Internal waves; Microstructure; Ocean basins; Ocean circulation; Ocean models; Oceans; Profiles; Satellite altimetry; Satellite observation; Satellites; Seamounts; Ships; Slope; Stations; Stratification; Tidal cycles; Tidal dynamics; Tidal energy; Tidal power; Tidal waves; Tides; Turbulent mixing; Upper ocean
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2019JC015156

Low‐mode internal waves propagate over large distances and provide energy for turbulent mixing when they break far from their generation sites. A realistic representation of the oceanic energy cycle in ocean and climate models requires a consistent implementation of their generation, propagation, and dissipation. Here we combine the long‐term mean energy flux from satellite altimetry with results from a 1/10° global ocean general circulation model that resolves the low modes of internal waves and in situ observations of stratification and horizontal currents to study energy flux and dissipation along a 1000 km internal tide beam in the eastern North Atlantic. Internal wave fluxes were estimated from twelve 36‐ to 48‐hr stations in along‐ and across‐beam direction to resolve both the inertial period and tidal cycle. The observed internal tide energy fluxes range from 5.9 kW m−1 near the generation sites to 0.5 kW m−1 at distant stations. Estimates of energy dissipation come from both finestructure and upper ocean microstructure profiles and range, vertically integrated, from 0.5 to 3.3 mW m−2 along the beam. Overall, the in situ observations confirm the internal tide pattern derived from satellite altimetry, but the in situ energy fluxes are more variable and decrease less monotonically along the beam. Internal tides in the model propagate over shorter distances compared to results from altimetry and in situ measurements, but more spatial details close the main generation sites are resolved. Plain Language Summary Internal tides are generated when a tidal wave strikes underwater hills, seamounts, or slopes. These internal waves carry energy through the oceans' basins and finally mix the water when they break. It is important for ocean and climate models to realistically simulate the behavior of these waves, because the patterns of mixing in the ocean matter for the climate. In this study we use observations from ships and satellites and the results of a global ocean model to calculate the transport and loss of energy by internal tidal waves in a region where they are particularly strong, south of the Azores islands in the northeast Atlantic. The tidal waves lose a part of their energy and cause some mixing along their path, but most of the energy remains several hundreds of kilometers away from their generation site. Internal tides in the model propagate over shorter distances compared to the observations from satellite and ships, but it resolves more spati