Recent advancements on the characterization of sub-mesoscale variability using satellite altimetry

Recent evidence from along-track Sea Surface Height (SSH) observations has demonstrated the capabilities of current generation altimeters to tease out the oceanic variability in the meso to submesoscale wavelength range. In this work we review the capabilities of different altimetry missions to characterize ocean variability in the submesoscale wavelength range (λ < 100 km). We take advantage of the latest waveform processing techniques developed at CLS and CNES (e.g. High Frequency Adjustment and other adaptative retracking techniques, SAR/LR-RMC, etc.). We use the characteristic scale that marks the shift from balanced-motion (eddy) dominated towards unbalanced-motion (wave) dominated in the SSH spectrum (Transition Scale; Lt) as a performance metric for the different missions. Higher signal to noise ratio is obtained due to the reprocessing techniques, enhancing the observability of fine scale variability. This results in an improvement of our estimates of Lt and its comparisons against modeling results. Our estimates of average Lt and its spatial distribution at global scale are in agreement with the values predicted by global models. The lowest values (Lt < 50 km) are found at the highly energetic western boundary current systems, marking a clear asymmetry with the eastern boundaries in all the ocean basins (Lt ~100-150 km). Lt values progressively increase from the mid-latitudes (~150 km) towards the equatorial ocean (Lt > 250 km), consistent with the increased dominance of unbalanced over balanced motions in the SSH variability that is observed at low latitudes. Limitations of our methodology and implications for the future wide-swath observations from SWOT are discussed.