How Realistic is the Internal Tide Energy Decay in a Global Ocean Model?

Maarten C Buijsman, University of Southern Mississippi, Stennis Space Center, MS, United States, Joseph K Ansong, Univ of MI-Earth & Environ Sci, Ann Arbor, MI, United States, SAND-Brian K Arbic, University of Michigan, Earth and Environmental Sciences, Ann Arbor, MI, United States, Mattias Green, Bangor University, School of Ocean Sciences, Bangor, LL59, United Kingdom, James G Richman, Naval Research Lab Stennis Space Center, Stennis Space Center, MS, United States, Jay F Shriver, Naval Research Laboratory, Stennis Space Center, Stennis Space Center, MS, United States, Gordon Stephenson, University of Southern Mississippi, Department of Marine Science, Stennis Space Center, MS, United States, Clément Vic, Laboratoire de Physique des Océans, Brest, France, Alan J Wallcraft, Florida State University, Center for Ocean-Atmospheric Prediction Studies, Tallahassee, FL, United States, Amy Frances Waterhouse, Scripps Institution of Oceanography, La Jolla, CA, United States, Caitlin B Whalen, Applied Physics Laboratory University of Washington, Seattle, WA, United States and Zhongxiang Zhao, University of Washington
Global ocean models with O(1 km) horizontal resolution begin to resolve internal waves with wave lengths of O(10 km). However, it is not yet clear how well these models handle the dissipation of the resolved low-mode waves in an eddying ocean. A better understanding of this may contribute to the development of dissipation parameterizations. We present model results from a realistically-forced global HYbrid Coordinate Ocean Model (HYCOM) simulation with a horizontal resolution of 4 km (1/25°) and 41 layers. Both surface and internal tides are dampened by a linear wave drag parameterization. We analyze the diurnal and semidiurnal surface and internal tide energetics and compare our results with altimetry, altimetry-inferred dissipation rates and energy fluxes, analytical barotropic to baroclinic conversion models, and microstructure and finescale dissipation rates. The model accurately predicts M2 surface tides to within 2.6 cm error. The dissipation as a fraction of the barotropic to baroclinic energy conversion is larger than 100% over three-quarters of the ocean area due to the dissipation of remotely generated internal tides. This is much larger than the 30% dissipation fraction used in climate model simulations. The mode-1 e-folding decay times are about 8 days to the north and south of the critical latitudes, implying that PSI has a minimal impact in our 4-km simulation. Our simulation agrees well with altimetry-inferred sea-surface height variance (see Figure) and surface tide dissipation, and analytical conversion models. However, the sum of the depth-integrated resolved low-mode and the parameterized high-mode dissipation is up to a factor of two larger than the depth-integrated dissipation rates inferred from finescale methods, but smaller than the dissipation rates from microstructure.