Improving the parameterizations of internal wave driven mixing from small scale turbulent observations to global climate model implementations

In the ocean interior, the internal wave field is largely responsible for connecting the forcing scales of the circulation to the dissipative scale of turbulence. In particular, internal-wave-induced mixing drives the diabatic evolution of the ocean’s stratification on the very time scales of central interest to the climate prediction problem. The Climate Process Team on internal wave driven mixing has been working over the last 5 years to refine, develop and implement dynamically appropriate parameterizations for diapycnal mixing due to internal-wave breaking for use in global climate models. The problem can be framed in terms of sources and sinks for internal waves. The main sources of internal wave energy in the ocean are internal tides and wind-generated internal waves. Both have a geography that has been well studied, though the latter has more complicated forcing variability. In both cases some of the energy put into the ocean tends to dissipate and produce mixing nearby, producing a global map of mixing that mirrors those of internal wave generation. This so-called “nearfield” part of the problem involves breaking of high-mode internal waves or more nonlinear features. The rest of the energy is able to propagate away, sometimes for thousands of kilometers, in the form of low-mode internal waves. The ultimate graveyard for the propagating part of the energy is less clear, although several possibilities are being actively investigated. Additionally, internal lee waves generated by mesoscale flows over rough topography may also be important energy sources in some locations, particularly the Southern Ocean. As a final conclusion, we attempt to put the sum of these processes in a global context using all available microstructure observations.