Wavenumber spectral slopes of sea surface height (SSH) and kinetic energy (KE) have been used to infer “interior” or surface quasi-geostrophic (QG or SQG) dynamics of the ocean. However, noise-corrected altimeter SSH in a fixed mesoscale band of 70 to 250 km have much flatter slopes than the QG or SQG predictions over most of the ocean. Spectra estimated from an eddy resolving global ocean circulation model (the HYbrid Coordinate Ocean Model) with embedded tides, suggest that the flatter slopes arise from two additional sources: (1) presence of strong internal waves and tides and (2) shift of the inertial sub-range to smaller scales. Separating the high and low frequency variability yields a different pattern with flatter spectra at high frequency and steeper spectrum at low frequency. For low mesoscale KE, the inertial subrange moves to smaller scales based upon the enstrophy spectra. Thus, it is difficult to infer the ocean dynamics from the altimeter spectral slope over a fixed wavenumber band.
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