Importance of damping in comparison of internal tides in several global hydrodynamical models with altimetry

Joseph K Ansong1, Brian K Arbic2, Dimitris Menemenlis3, Alan J Wallcraft4, Romain Bourdalle-Badie5, Jerome Chanut6, Frederic Briol7, Michael Schindelegger8, Richard Ray9, Eric P. Chassignet10, Robert Hallberg11, Loren Carrère12, Gérald Dibarboure13, Nicolas Picot13, Maarten C Buijsman14, James G Richman15, Jay F Shriver16, Christopher N Hill17, Matthew R Mazloff18, Rui M Ponte19, Ariane Koch-Larrouy20, Florent Lyard20 and An T Nguyen21, (1)University of Ghana, Department of Mathematics, Accra, Ghana, (2)University of Michigan, Earth and Environmental Sciences, Ann Arbor, MI, United States, (3)NASA Jet Propulsion Laboratory, Pasadena, United States, (4)Florida State University, Center for Ocean-Atmospheric Prediction Studies, Tallahassee, FL, United States, (5)Mercator Ocean international, Ramonville Saint-Agne, France, (6)Mercator Ocean International, Ramonville Saint-Agne, France, (7)Collecte Localisation Satellites, Ramonville-Saint-Agne, France, (8)University of Bonn, Institute of Geodesy and Geoinformation, Bonn, Germany, (9)NASA Goddard Space Flight Center, Geodesy & Geophysics Lab, Greenbelt, MD, United States, (10)Center for Ocean-Atmospheric Prediction Studies, Florida State University, Tallahassee, FL, United States, (11)NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, NJ, United States, (12)CLS, Ramonville Saint-Agne, France, (13)CNES French National Center for Space Studies, Toulouse Cedex 09, France, (14)University of Southern Mississippi, Stennis Space Center, MS, United States, (15)Naval Research Lab Stennis Space Center, Stennis Space Center, MS, United States, (16)Naval Research Laboratory, Stennis Space Center, Stennis Space Center, MS, United States, (17)MIT, Cambridge, United States, (18)Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, United States, (19)Atmospheric and Environmental Research, Lexington, MA, United States, (20)LEGOS, Toulouse, France, (21)University of Texas at Austin, Institute of Computational Engineering and Sciences, Austin, TX, United States
High-resolution global hydrodynamical models that contain both eddies and internal waves are becoming increasingly useful for the SWOT mission. It is therefore important to know how well such models compare to observations. Here we focus on the ability of four such models to reproduce the internal tide sea surface height signature seen in nadir altimeters. These include simulations from the HYbrid Coordinate Ocean Model (HYCOM), the Modular Ocean Model Version 6 (MOM6), the Nucleus for European Modelling of the Ocean (NEMO), and the Massachussetts Institude of Technology general circulation model (MITgcm). Consistent with a previous study that employed only the HYCOM model, we find that the absence of an explicit damping mechanism on tidal flows in global ocean models results in internal tides that are too energetic and propagate too far from their sources. We also find that the length of model output used in harmonic analysis impacts the comparison of internal tide amplitudes to those derived from along-track satellite altimetry, consistent with the previous investigation. Differences in internal tide strength in different models run at the same resolution, and without additional explicit damping, are likely due to differences in numerics amongst the models, although further study is needed to confirm this. This paper also documents, for the first time, some details of the tidal forcing in the particular MITgcm runs examined here, that adversely affect the accuracies of the modeled tides, and suggests correction factors using less expensive barotropic shallow-water simulations that roughly mimic the tidal forcing in the MITgcm runs.