How to Improve Surface and Internal Tides in a Global Ocean Model? Use a Linear Wave Drag Parameterization!
Maarten C Buijsman1, Joseph K Ansong2, Brian K Arbic2, James G Richman3, Jay F Shriver4, Patrick G Timko5, Alan J Wallcraft6, Caitlin Beth Whalen7 and Zhongxiang Zhao8, (1)University of Southern Mississippi, Stennis Space Center, MS, United States, (2)University of Michigan Ann Arbor, Ann Arbor, MI, United States, (3)COAPS, Florida State University, Tallahassee, FL, United States, (4)Naval Research Laboratory, Stennis Space Center, Stennis Space Center, MS, United States, (5)University of Michigan, Dept of Earth and Environmental Sciences, Ann Arbor, MI, United States, (6)Naval Research Laboratory, Stennis Space Center, MS, United States, (7)University of California San Diego, La Jolla, CA, United States, (8)Applied Physics Laboratory University of Washington, Seattle, WA, United States
Abstract:
The effects of a parameterized linear internal wave drag on the semidiurnal barotropic and baroclinic energetics of realistically forced three-dimensional global ocean models with 4 and 8 km horizontal resolutions are analyzed. Although the main purpose of the parameterization is to improve the surface tides, it also influences the internal tides. The coarse resolution of global ocean models only permits the generation and propagation of the lowest vertical modes. Hence, the wave drag parameterization represents the energy conversion to and the subsequent breaking of the unresolved high modes. We will discuss the impact of the horizontal resolution on the energetics, the generation of the vertical modes, and the wave drag strength.
Findings for the 8-km model indicate a reasonable agreement of the surface and internal tide energetics with TPXO, an accurate satellite-altimetry constrained model, Argo floats, and satellite altimetry. In addition to the surface tides, the wave drag also damps the low-mode internal tides as they propagate away from their generation sites. Hence, it can be considered a scattering parameterization, causing more than 50% of the deep water dissipation of the internal tides in the 8-km model. The good agreement between the internal tide predictions in the 8-km model and satellite altimetry confirms that a wave-drag parameterization is required to prevent overly energetic internal tides. We use a plane-wave fitting technique to estimate the amount of low-mode energy that reaches the shelves. Realistically forced global ocean models with accurate internal tides may provide crucial input for climate models on the amount and location of internal tide dissipation.
