Seasonality and spatial dependence of meso- and submesoscale ocean currents from satellite altimetry

Submesoscale flows have been seen in simulations and shipboard data to exhibit qualitative seasonal changes, consistent with submesoscale baroclinic instabilities being activated in deep winter mixed layers. To further test and understand this, we use Jason-2/OSTM satellite data to compute along-track sea surface height (SSH) spectra across the global ocean, for each calendar month. The balanced flow is modeled by a low-wavenumber plateau transitioning to a submesoscale power-law falloff. When tides are weak, we find statistically significant variation with location and season in the parameters describing balanced motion. Our model of the signal and altimeter noise produces a power-law falloff which is closer to the results of numerical models and in situ measurements as compared to prior altimetry-based studies. The power law exponent decreases in the winter and increases in the summer, and there is evidence of kinetic energy moving upwards to larger scales in the months following the month of maximum mixed layer depth. This correlates with the deepening and shoaling of the mixed layer (computed from climatology) and is consistent with shipboard ADCP data.