Meso- to Submesoscale Turbulence in the Ocean

The energy cycle in ocean models is still biased due to the large uncertainty regarding how processes in the mesoscale and submesoscale regimes are represented. Since mesoscale turbulence is largely geostrophic, it features an energy transfer towards larger scales. In contrast, submesoscale turbulence can contain both geostrophic and ageostrophic dynamics which makes the direction of the energy flux less clear. Measuring the kinetic energy spectrum in the ocean is challenging, since gridded satellite data are unable to resolve the subdeformation scales, and shipboard measurements are limited to a few regions. Lagrangian floats are globally available, can connect a range of scales from 10 m to 1000 km and hence are a unique source of information on meso- to submesoscale turbulence.
We estimate the kinetic energy spectral flux from SSH data which gives only the geostrophic part, compared to spectral fluxes from a submesoscale permitting ocean model with a focus on the North Atlantic.
The kinetic energy spectral fluxes are found to exhibit both inverse and forward cascade, with a higher inverse cascade in turbulent areas and maximum inverse wavenumber increasing with latitude.
In addition, we calculate velocity structure functions from the surface drifter data to bridge different scales, with the goal to compare and contrast the spectral estimates of different data sets. Velocity structure functions are the moments of velocity increments between two points and provide information about the properties of turbulent dynamics at different scales.