Atmosphere Ocean Science Colloquium

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The Role of Mixed Layer Instabilities in Submesoscale Turbulence

Speaker: Jorn Callies, MIT

Location: Warren Weaver Hall 1302

Date: Wednesday, September 30, 2015, 3:30 p.m.

Synopsis:

Upper-ocean turbulence at scales smaller than the mesoscale is believed to exchange surface and thermocline waters, which plays an important role in both physical and biogeochemical budgets. But the dynamics that energize this submesoscale turbulence remain a topic of debate. Models and observations suggest that baroclinic mixed layer instabilities play an important role and energize submesoscale flows in winter. The goal here is to understand the essence of this energization, using a simple Eady-like quasi-geostrophic model. The model captures the scale and structure of the linear mixed layer instability. A turbulent inverse cascade of kinetic energy arises in the nonlinear regime and energizes a wide range of scales. The resulting distribution of energy across scales and in the vertical compares favorably to observations of energetic wintertime submesoscale flows, suggesting that the simple model captures the leading-order balanced dynamics of these flows. Caveats and implications of the dynamics described by the model will be discussed.