Estimates of wind power and radiative near-inertial internal wave flux

Abstract

Energy transfer mechanisms between the atmosphere and the deep ocean have been studied for many years. Their importance to the ocean’s energy balance and possible implications on mixing are widely accepted. The slab model by Pollard (Deep-Sea Res Oceanogr Abstr 17(4):795–812, 1970) is a well-established simulation of near-inertial motion and energy inferred through wind-ocean interaction. Such a model is set up with hourly wind forcing from the NCEP-CFSR reanalysis that allows computations up to high latitudes without loss of resonance. Augmenting the one-dimensional model with the horizontal divergence of the near-inertial current field leads to direct estimates of energy transfer spectra of internal wave radiation from the mixed layer base into the ocean interior. Calculations using this hybrid model are carried out for the North Atlantic during the years 1989 and 1996, which are associated with positive and negative North Atlantic Oscillation index, respectively. Results indicate a range of meridional regimes with distinct energy transfer ratios. These are interpreted in terms of the mixed layer depth, the buoyancy frequency at the mixed layer base, and the wind field structure. The average ratio of radiated energy fluxes from the mixed layer to near-inertial wind power for both years is approximately 12%. The dependence on the wind structure is supported by simulations of idealized wind stress fronts with variable width and translation speeds.

Spatial and seasonal variations of near-inertial kinetic energy in the upper Ross Sea and the controlling factors

“…In addition to the aforementioned influencing factors, previous studies showed that the ratio of the near-inertial energy fluxes radiated to the ocean interior is theoretically proportional to the buoyancy frequency at the mixed layer base (e.g., Voelker et al, 2020). Therefore, the NIKE in the surface mixed layer, which is the radiated NIKE subtracted from the total injected wind energy, should also be related to the buoyancy frequency.…”

Time Series of Near‐Inertial Gravity Wave Energy Fluxes: The Effect of a Strong Wind Event

“…Voelker et al. (2020) found a dependence on wind work and mixed layer depth, with a mean energy transfer to the internal wavefield of 12% in the North Atlantic. Alford (2020b) found values of 12% and 17% by using a Price‐Weller‐Pinkel mixed layer model, and further suggests that the energy available for deep‐ocean mixing from near‐inertial waves is reduced in importance relative to internal tides, although the greater shear of near‐inertial waves for the same energy relative to internal tides may still allow them to play a role.…”