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Published September 2022 | public
Journal Article

Seasonality and Spatial Dependence of Mesoscale and Submesoscale Ocean Currents from Along-Track Satellite Altimetry


Along-track wavenumber spectral densities of sea surface height (SSH) are estimated from Jason-2 altimetry data as a function of spatial location and calendar month to understand the seasonality of meso- and submesoscale balanced dynamics across the global ocean. Regions with significant mode-1 and mode-2 baroclinic tides are rejected, restricting the analysis to the extratropics. Where balanced motion dominates, the SSH spectral density is averaged over all pass segments in a region for each calendar month and is fit to a four-parameter model consisting of a flat plateau at low wavenumbers, a transition at wavenumber k₀ to a red power law spectrum k⁻⁵, and a white spectrum at high wavenumbers that models the altimeter noise. The monthly time series of the model parameters are compared to the evolution of the mixed layer. The annual mode of the spectral slope s reaches a minimum after the mixed layer deepens, and the annual mode of the bandpassed kinetic energy in the ranges [2k₀, 4k₀] and [k₀, 2k₀] peak ~2 and ~4 months, respectively, after the maximum of the annual mode of the mixed layer depth. This analysis is consistent with an energization of the submesoscale by a winter mixed layer instability followed by an inverse cascade of kinetic energy to the mesoscale, in agreement with prior modeling studies and in situ measurements. These results are compared to prior modeling, in situ, and satellite investigations of specific regions and are broadly consistent with them within measurement uncertainties.

Additional Information

We thank Weiguang Wu for sharing his code. We thank Dhruv Balwada and, Jacob Steinberg for useful discussions. The work of A.L. was supported by a Provost's Research Innovation Award from Brandeis University. This work was initiated while A.L. was at the Kavli Institute for Theoretical Physics, which is supported by National Science Foundation Grant NSF PHY-1748958; it was also performed in part at the Aspen Center for Physics, which is supported by National Science Foundation Grant PHY-1607611. J.C. was supported by NASA Grant 80NSSC20K1140.

Additional details

August 22, 2023
October 23, 2023