Frequency, Wavenumber, and Spatial Decomposition of Sea-Surface-Height Estimates From an Ocean Reanalysis

By assimilating WOCE hydrography, TOPEX/POSEIDON, and other satellite and in-situ data, ocean reanalyses improve several aspects of the ocean circulation relative to simulations. Here we describe and quantify changes in sea-surface height anomaly, region-by-region, and in 12 distinct frequency-wavenumber bands, obtained through 2D, finite-impulse-response filters, for a reanalysis carried out by the ECCO (Estimating the Circulation and Climate of the Ocean, http://www.ecco-group.org) consortium. These bands span, respectively, the large scale, non-propagating signal, Rossby waves at periods of 24, 12, 6, and 3-months, Kelvin waves at periods of 6, 3, and 1.5 months, tropical instability waves, and eddies. We aim to associate changes in individual model parameters and forcing fields to changes in specific bands of the 2D spectrum. Overall, the variance of the simulation is too weak by a factor of two or more; the ECCO reanalysis has variability that is closer to, though still weaker than, that of TOPEX-POSEIDON. The model/data variance discrepancy is not equally distributed in the spectrum; some frequency bands are better reproduced than others. Most of the improvement is attributable to winds, but buoyancy fluxes and internal model parameters also play a role. This study provides insight on model representation errors as well as on the generation and dissipation mechanisms of planetary waves.