Surface and Sub-Surface Kinetic Energy Wavenumber-Frequency Spectra in Global Ocean Models and Observations

This paper examines spectra of horizontal kinetic energy (HKE) in the surface and sub-surface ocean, with an emphasis on internal gravity wave (IGW) motions, in global high-resolution ocean simulations. Horizontal wavenumber-frequency spectra of surface HKE are computed over seven oceanic regions from two global simulations of the HYbrid Coordinate Ocean Model (HYCOM) and three global simulations of the Massachusetts Institute of Technology general circulation model (MITgcm). In regions with high IGW activity, high surface HKE variance in the horizontal wavenumber-frequency spectra is aligned along IGW linear dispersion curves. For both HYCOM and MITgcm, and in almost all regions, finer horizontal resolution yields more energetic supertidal IGW continuum spectra. The ratio of high-horizontal-wavenumber variance in semi-diurnal and supertidal motions relative to lower-frequency motions, a quantity of great interest for swath altimetry, depends on the model employed and the horizontal resolution within the model, implying that quantitative predictions of the partition between low- and high-frequency motions taken from particular simulations should be treated with care. The frequency-vertical wavenumber spectra, frequency spectra, and vertical wavenumber spectra from the models are compared to spectra computed from McLane profilers at nine locations. In general, MITgcm spectra match the McLane profiler spectra more closely at high frequencies (|omega| > 4.5 cpd). In both models, vertical wavenumber spectra roll off more steeply than observations at high vertical wavenumbers (m > 10(-2) cpm). The vertical wavenumber spectra in such models is an important target for improvement, due to turbulence production and dissipation that takes place at high vertical wavenumbers.