Stimulated imbalance and the enhancement of eddy kinetic energy dissipation by internal waves

Barkan, R, Winters KB, McWilliams JC.  2017.  Stimulated imbalance and the enhancement of eddy kinetic energy dissipation by internal waves. Journal of Physical Oceanography. 47:181-198.

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antarctic circumpolar current, balance, energetics, generation, geostrophic flow, instability, mesoscale, model, ocean inertial motions, wind


The effects of internal waves (IWs), externally forced by high-frequency wind, on energy pathways are studied in submesoscale-resolving numerical simulations of an idealized wind-driven channel flow. Two processes are examined: the direct extraction of mesoscale energy by externally forced IWs followed by an IW forward energy cascade to dissipation and stimulated imbalance, a mechanism through which externally forced IWs trigger a forward mesoscale to submesoscale energy cascade to dissipation. This study finds that the frequency and wavenumber spectral slopes are shallower in solutions with high-frequency forcing compared to solutions without and that the volume-averaged interior kinetic energy dissipation rate increases tenfold. The ratio between the enhanced dissipation rate and the added high-frequency wind work is 1.3, demonstrating the significance of the IW-mediated forward cascades. Temporal-scale analysis of energy exchanges among low-(mesoscale), intermediate-(submesoscale), and high-frequency (IW) bands shows a corresponding increase in kinetic energy E-k and available potential energy APE transfers from mesoscales to submesoscales (stimulated imbalance) and mesoscales to IWs (direct extraction). Two direct extraction routes are identified: a mesoscale to IW Ek transfer and a mesoscale to IW APE transfer followed by an IW APE to IW Ek conversion. Spatial-scale analysis of eddy-IW interaction in solutions with high-frequency forcing shows an equivalent increase in forward Ek and APE transfers inside both anticyclones and cyclones.