קולוקוויום בחוג לגאופיזיקה: Breaking the Balance: Mechanisms of Oceanic Kinetic Energy Transfers from Geostrophic to Ageostrophic Motions

Zoom: https://tau-ac-il.zoom.us/j/85032703038

Abstract:

The ocean's most energetic currents and mesoscale eddies are largely in geostrophic balance, and the energy contained in these so-called ‘balanced’ flows tends to cascade toward larger scales. Yet, for the climate system to reach equilibrium, this energy must ultimately cascade towards smaller scales where it can be dissipated. Understanding the mechanisms leading to ‘loss of balance’ is therefore important for better modelling and predicting the ocean’s role in the climate system. This dissertation investigates three pathways through which energy moves from balanced mesoscale flows to unbalanced submesoscale motions and internal waves. First, a reduced physical model of a sharpening ocean front reveals how internal waves trapped within the front can extract energy from the balanced flow, exposing a previously unrecognized convergent-production mechanism that becomes dominant as the front intensifies. Second, linear stability analysis demonstrates that, as fronts strengthen, their dominant instability shifts from classical baroclinic instability to an effective inertia critical-layer instability produced by resonance between Rossby and internal wave modes. In this regime, shear production becomes as energetically important as buoyancy flux, revealing a limitation of existing mixed-layer parameterizations and illustrating another route for ‘loss of balance’. Finally, high-resolution simulations show that anticyclonic eddies can spontaneously emit spiraling internal waves through radiative instability, providing a direct route from mesoscale balanced motion to unbalanced internal waves. Together, these results provide a unified framework for understanding how balanced ocean flows become unbalanced and offer guidance for improving the representation of mixing and energy transfer in ocean circulation models.

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מארגן האירוע: ד"ר ליאור רובננקו