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On the modifications of near-inertial waves at fronts: implications for energy transfer across scales

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Abstract

In the ocean, wind-generated kinetic energy (KE) manifests itself primarily in balanced currents and near-inertial waves. The dynamics of these flows is strongly constrained by the Earth’s rotation, causing the KE in balanced currents to follow an inverse cascade but also preventing wave-wave interactions from fluxing energy in the near-inertial band to lower frequencies and higher vertical wavenumbers. How wind-generated KE is transferred to small-scale turbulence and dissipated is thus a non-trivial problem. This article presents a review of recent theoretical calculations and numerical simulations that demonstrate how some surprising modifications to internal wave physics by the lateral density gradients present at ocean fronts allow for strong interactions between balanced currents and near-inertial waves that ultimately result in energy loss for both types of motion.

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Notes

  1. This expression for f e f f is only valid for straight fronts. If the front is curved, inertial motions oscillate at a frequency that depends on the flow curvature as well, see for example Kunze and Boss (1998).

  2. Note that since the front is two-dimensional, there is no geostrophic flow nor thermal wind shear in the y-direction.

  3. This is true for a front with upward sloping isopycnals where v ′ and w ′ are positively correlated as shown in Fig. 3, and as used in the stability analysis plotted in Fig. 4. When isopycnals slope downward, the times of maximum inertial shear and maximum |v ′| must coincide for PSI to develop since v ′ and w ′ are anti-correlated in that case.

  4. Note that for this simple frontal zone without vertical vorticity, the slope of M −surfaces is s M = f 2/S 2 = R i g s ρ . Hence as R i g → 1, s M approaches the isopycnal slope s ρ .

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Acknowledgements

This article reviews material that I was invited to present at the 48th Liege Colloquium on Submesoscale Processes: Mechanisms, Implications and New Frontiers. I would like to thank Alexander Barth, Eric Deleesnijder, Amala Mahadevan, Ananda Pascual, Simon Ruiz, and Charles Troupin for organizing such a stimulating meeting and inviting me to speak. This work was funded by the National Science Foundation grant OCE-1260312.

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  1. Department of Earth System Science, Stanford University, Stanford, CA, USA

    Leif N. Thomas

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Correspondence to Leif N. Thomas.

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Responsible Editor: Amala Mahadevan

This article is part of the Topical Collection on the 48th International Liège Colloquium on Ocean Dynamics, Liège, Belgium, 23–27 May 2016

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Thomas, L. On the modifications of near-inertial waves at fronts: implications for energy transfer across scales. Ocean Dynamics 67, 1335–1350 (2017). https://doi.org/10.1007/s10236-017-1088-6

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