Atmosphere Ocean Science Friday Seminar

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Wave-induced laminar flows in zonally-dominated turbulence

Speaker: Norman Cao, CIMS

Location: Warren Weaver Hall 1314

Date: Friday, February 17, 2023, 4 p.m.

Synopsis:

In seeming contradiction to the conception of turbulence as a mixing phenomenon, turbulent systems can sometimes exhibit the spontaneous emergence of structured coherent flows. A key example are the large-scale zonal jets which form in magnetically confined fusion plasmas and in planetary atmospheres. Studying turbulence in such systems is challenging, as the structure and memory of the coherent flows resist statistically homogeneous description.

In this talk, I will present a computational and theoretical study of coherence in turbulent flows in the barotropic beta-plane quasigeostrophic (QG) equations, a prototypical two-dimensional model for turbulence in Jovian atmospheres. It will be shown how the large-scale Rossby wave component of these flows can be characterized as "nearly-integrable" perturbations to the coherent zonal flow Lagrangian dynamics, linking finite-dimensional Hamiltonian chaos in the plane to a laminar-to-turbulent flow transition. Techniques from dynamical systems reveal that the Lagrangian flows induced by the zonal flows plus large-scale waves exhibit localized chaotic regions bounded by invariant tori, manifesting as a spatially inhomogeneous wave-induced turbulent mixing. It is argued that the surviving invariant tori organize the large-scale flows into a single temporally and zonally varying laminar flow, suggesting a form of self-organization that can account for the signature of linear Rossby waves in fully-developed turbulence.